Summary
A powerful and robust templating system for Python.
Overview
EmPy is a system for embedding Python expressions and statements
in template text; it takes an EmPy source file, processes it, and
produces output. This is accomplished via expansions, which are
special signals to the EmPy system and are set off by a special
prefix (by default the at sign, '@'). EmPy can expand arbitrary
Python expressions and statements in this way, as well as a
variety of special forms. Textual data not explicitly delimited
in this way is sent unaffected to the output, allowing Python to
be used in effect as a markup language. Also supported are
callbacks via hooks, recording and playback via diversions, and
dynamic, chainable filters. The system is highly configurable via
command line options and embedded commands.
Expressions are embedded in text with the '@(...)' notation;
variations include conditional expressions with '@(...?...!...)'
and the ability to handle thrown exceptions with '@(...$...)'. As
a shortcut, simple variables and expressions can be abbreviated as
'@variable', '@object.attribute', '@function(arguments)',
'@sequence' [index], and combinations. Full-fledged statements
are embedded with '@{...}'. Control flow in terms of conditional
or repeated expansion is available with '@[...]'. A '@' followed
by a whitespace character (including a newline) expands to
nothing, allowing string concatenations and line continuations.
Comments are indicated with '@#' and consume the rest of the line,
up to and including the trailing newline. '@%' indicate
"significators," which are special forms of variable assignment
intended to specify per-file identification information in a
format which is easy to parse externally. Context name and line
number changes can be done with '@?' and '@!' respectively.
'@<...>' markups are customizeable by the user and can be used for
any desired purpose. Escape sequences analogous to those in C can
be specified with '@\...', and finally a '@@' sequence expands to
a single literal at sign.
Getting the software
The current version of empy is 3.3.
The latest version of the software is available in a tarball here:
"http://www.alcyone.com/software/empy/empy-latest.tar.gz",
http://www.alcyone.com/software/empy/empy-latest.tar.gz.
The official URL for this Web site is
"http://www.alcyone.com/software/empy/",
http://www.alcyone.com/software/empy/.
Requirements
EmPy should work with any version of Python from 1.5.2 onward. It
has been tested with all major versions of CPython from 1.5 up,
and Jython from 2.0 up (using Java runtimes 1.3 and 1.4). The
included test script is intended to run on Unix-like systems with
a Bourne shell.
License
This code is released under the "LGPL",
http://www.gnu.org/copyleft/lesser.html.
Mailing lists
There are two EmPy related mailing lists available. The first is
a receive-only, very low volume list for important announcements
(including releases). To subscribe, send an email to
"empy-announce-list-subscribe@alcyone.com",
mailto:empy-announce-list-subscribe@alcyone.com.
The second is a general discussion list for topics related to
EmPy, and is open for everyone to contribute; announcements
related to EmPy will also be made on this list. The author of
EmPy (and any future developers) will also be on the list, so it
can be used not only to discuss EmPy features with other users,
but also to ask questions of the author(s). To subscribe, send an
email to "empy-list-subscribe@alcyone.com",
mailto:empy-list-subscribe@alcyone.com.
Basics
EmPy is intended for embedding Python code in otherwise
unprocessed text. Source files are processed, and the results are
written to an output file. Normal text is sent to the output
unchanged, but markups are processed, expanded to their results,
and then written to the output file as strings (that is, with the
'str' function, not 'repr'). The act of processing EmPy source
and handling markups is called "expansion."
Code that is processed is executed exactly as if it were entered
into the Python interpreter; that is, it is executed with the
equivalent of 'eval' (for expressions) and 'exec' (for
statements). EmPy is intended to be a very thin (though powerful)
layer on top of a running Python system; Python and EmPy files can
be mixed together (via command line options) without
complications.
By default the embedding prefix is the at sign ('@'), which
appears neither in valid Python code nor commonly in arbitrary
texts; it can be overridden with the -p option (or with the
'empy.setPrefix' function). The prefix indicates to the EmPy
interpreter that a special sequence follows and should be
processed rather than sent to the output untouched (to indicate a
literal at sign, it can be doubled as in '@@').
When the interpreter starts processing its target file, no modules
are imported by default, save the 'empy' pseudomodule (see below),
which is placed in the globals; the 'empy' pseudomodule is
associated with a particular interpreter -- in fact, they are the
same object -- and it is important that it not be removed from
that interpreter's globals, nor that it be shared with other
interpreters running concurrently (a name other than 'empy' can be
specified with the -m option). The globals are not cleared or
reset in any way. It is perfectly legal to set variables or
explicitly import modules and then use them in later markups,
*e.g.*, '@{import time} ... @time.time()'. Scoping rules are as
in normal Python, although all defined variables and objects are
taken to be in the global namespace.
Indentation is significant in Python, and therefore is also
significant in EmPy. EmPy statement markups ('@{...}'), when
spanning multiple lines, must be flush with the left margin. This
is because (multiline) statement markups are not treated specially
in EmPy and are simply passed to the Python interpreter, where
indentation is significant.
Activities you would like to be done before any processing of the
main EmPy file can be specified with the -I, -D, -E, -F, and -P
options. -I imports modules, -D executes a Python variable
assignment, -E executes an arbitrary Python (not EmPy) statement,
-F executes a Python (not EmPy) file, and -P processes an EmPy
(not Python) file. These operations are done in the order they
appear on the command line; any number of each (including, of
course, zero) can be used.
Expansions
The following markups are supported. For concreteness below, '@'
is taken for the sake of argument to be the prefix character,
although this can be changed.
**'@# COMMENT NEWLINE'** -- A comment. Comments, including the
trailing newline, are stripped out completely. Comments should
only be present outside of expansions. The comment itself is
not processed in any way: It is completely discarded. This
allows '@#' comments to be used to disable markups. *Note:* As
special support for "bangpaths" in Unix-like operating systems,
if the first line of a file (or indeed any context) begins with
'#!', and the interpreter has a 'processBangpaths' option set to
true (default), it is treated as a '@#' comment. A '#!'
sequence appearing anywhere else will be handled literally and
unaltered in the expansion. Example::
@# This line is a comment.
@# This will NOT be expanded: @x.
**'@? NAME NEWLINE'** -- Set the name of the current context to be
the given string. Variables are not allowed here; the name is
treated as a literal. (If you wish to use arbitrary
expressions, use the 'empy.setContextName' function instead.)
Example::
@?NewName
The context name is now @empy.identify()[0] (NewName).
**'@! INTEGER NEWLINE'** -- Set the line number of the current
context to be the given integer value; this is similar to the
'#line' C preprocessor directive. This is done in such a way
that the *next* line will have the specified numeric value, not
the current one. Expressions are not allowed here; the number
must be a literal integer. (If you wish to use arbitrary
expressions, use the 'empy.setContextLine' function instead.)
Example::
@!100
The context line is now @empy.identify()[1] (100).
**'@ WHITESPACE'** -- A '@' followed by one whitespace character
(a space, horizontal tab, vertical tab, carriage return, or
newline) is expanded to nothing; it serves as a way to
explicitly separate two elements which might otherwise be
interpreted as being the same symbol (such as '@name@ s' to mean
'@(name)s' -- see below). Also, since a newline qualifies as
whitespace here, the lone '@' at the end of a line represents a
line continuation, similar to the backslash in other languages.
Coupled with statement expansion below, spurious newlines can be
eliminated in statement expansions by use of the '@{...}@'
construct. Example::
This will appear as one word: salt@ water.
This is a line continuation; @
this text will appear on the same line.
**'@\ ESCAPE_CODE'** -- An escape code. Escape codes in EmPy are
similar to C-style escape codes, although they all begin with
the prefix character. Valid escape codes include:
'@\0' -- NUL, null
'@\a' -- BEL, bell
'@\b' -- BS, backspace
'@\d' -- three-digital decimal code DDD
'@\e' -- ESC, escape
'@\f' -- FF, form feed
'@\h' -- DEL, delete
'@\n' -- LF, linefeed character, newline
'@\oOOO' -- three-digit octal code OOO
'@\qQQQQ' -- four-digit quaternary code QQQQ
'@\r' -- CR, carriage return
'@\s' -- SP, space
'@\t' -- HT, horizontal tab
'@\v' -- VT, vertical tab
'@\xHH' -- two-digit hexadecimal code HH
'@\z' -- EOT, end of transmission
'@^X' -- the control character ^X
Unlike in C-style escape codes, escape codes taking some number
of digits afterward always take the same number to prevent
ambiguities. Furthermore, unknown escape codes are treated as
parse errors to discourage potential subtle mistakes. Note
that, while '@\0' represents the NUL character, to represent an
octal code, one must use '@\o...', in contrast to C. Example::
This embeds a newline.@\nThis is on the following line.
This beeps!@\a
There is a tab here:@\tSee?
This is the character with octal code 141: @\o141.
**'@@'** -- A literal at sign ('@'). To embed two adjacent at
signs, use '@@@@', and so on. Any literal at sign that you wish
to appear in your text must be written this way, so that it will
not be processed by the system. *Note:* If a prefix other than
'@' has been chosen via the command line option, one expresses
that literal prefix by doubling it, not by appending a '@'.
Example::
The prefix character is @@.
To get the expansion of x you would write @@x.
**'@)', '@]', '@}'** -- These expand to literal close parentheses,
close brackets, and close braces, respectively; these are
included for completeness and explicitness only. Example::
This is a close parenthesis: @).
**'@"..."', '@"""..."""', etc.** -- These string literals expand
to the literals themselves, so '@"test"' expands to 'test'.
Since they are inherently no-operations, the only reason for
their use is to override their behavior with hooks.
**'@( EXPRESSION )'** -- Evaluate an expression, and expand with
the string (via a call to 'str') representation evaluation of
that expression. Whitespace immediately inside the parentheses
is ignored; '@( expression )' is equivalent to '@(expression)'.
If the expression evaluates to 'None', nothing is expanded in
its place; this allows function calls that depend on side
effects (such as printing) to be called as expressions. (If you
really *do* want a 'None' to appear in the output, then use the
Python string '"None"'.) *Note:* If an expression prints
something to 'sys.stdout' as a side effect, then that printing
will be spooled to the output *before* the expression's return
value is. Example::
2 + 2 is @(2 + 2).
4 squared is @(4**2).
The value of the variable x is @(x).
This will be blank: @(None).
**'@( TEST ? THEN (! ELSE)_opt ($ EXCEPT)_opt )'** -- A special
form of expression evaluation representing conditional and
protected evaluation. Evaluate the "test" expression; if it
evaluates to true (in the Pythonic sense), then evaluate the
"then" section as an expression and expand with the 'str' of
that result. If false, then the "else" section is evaluated and
similarly expanded. The "else" section is optional and, if
omitted, is equivalent to 'None' (that is, no expansion will
take place). *Note*: For backward compatibility, the "else"
section delimiter, '!', may be expressed as a ':'. This
behavior is supported but deprecated.
If the "except" section is present, then if any of the prior
expressions raises an exception when evaluated, the expansion
will be replaced with the evaluation of the except expression.
(If the "except" expression itself raises, then that exception
will be propagated normally.) The except section is optional
and, if omitted, is equivalent to 'None' (that is, no expansion
will take place). An exception (cough) to this is if one of
these first expressions raises a SyntaxError; in that case the
protected evaluation lets the error through without evaluating
the "except" expression. The intent of this construct is to
except runtime errors, and if there is actually a syntax error
in the "try" code, that is a problem that should probably be
diagnosed rather than hidden. Example::
What is x? x is @(x ? "true" ! "false").
Pluralization: How many words? @x word@(x != 1 ? 's').
The value of foo is @(foo $ "undefined").
Division by zero is @(x/0 $ "illegal").
**'@ SIMPLE_EXPRESSION'** -- As a shortcut for the '@(...)'
notation, the parentheses can be omitted if it is followed by a
"simple expression." A simple expression consists of a name
followed by a series of function applications, array
subscriptions, or attribute resolutions, with no intervening
whitespace. For example:
- a name, possibly with qualifying attributes (*e.g.*,
'@value', '@os.environ').
- a straightforward function call (*e.g.*, '@min(2, 3)',
'@time.ctime()'), with no space between the function name
and the open parenthesis.
- an array subscription (*e.g.*, '@array[index]',
'@os.environ[name]', with no space between the name and
the open bracket.
- any combination of the above (*e.g.*,
'@function(args).attr[sub].other[i](foo)').
In essence, simple expressions are expressions that can be
written ambiguously from text, without intervening space. Note
that trailing dots are not considered part of the expansion
(*e.g.*, '@x.' is equivalent to '@(x).', not '@(x.)', which
would be illegal anyway). Also, whitespace is allowed within
parentheses or brackets since it is unambiguous, but not between
identifiers and parentheses, brackets, or dots. Explicit
'@(...)' notation can be used instead of the abbreviation when
concatenation is what one really wants (*e.g.*, '@(word)s' for
simple pluralization of the contents of the variable 'word').
As above, if the expression evaluates to the 'None' object,
nothing is expanded. Note that since a curly appearing where
EmPy would expect an open parenthesis or bracket in is
meaningless in Python, it is treated as a parse error (*e.g.*,
'@x{1, 2}' results in an error). Example::
The value of x is @x.
The ith value of a is @a[i].
The result of calling f with q is @f(q).
The attribute a of x is @x.a.
The current time is @time.ctime(time.time()).
The current year is @time.localtime(time.time())[0].
These are the same: @min(2,3) and @min(2, 3).
But these are not the same: @min(2, 3) vs. @min (2, 3).
The plural of @name is @(name)s, or @name@ s.
**'@` EXPRESSION `'** -- Evaluate a expression, and expand with
the 'repr' (instead of the 'str' which is the default) of the
evaluation of that expression. This expansion is primarily
intended for debugging and is unlikely to be useful in actual
practice. That is, a '@`...`' is identical to '@(repr(...))'.
Example::
The repr of the value of x is @`x`.
This print the Python repr of a module: @`time`.
This actually does print None: @`None`.
**'@: EXPRESSION : DUMMY :'** -- Evaluate an expression and then
expand to a '@:', the original expression, a ':', the evaluation
of the expression, and then a ':'. The current contents of the
dummy area are ignored in the new expansion. In this sense it
is self-evaluating; the syntax is available for use in
situations where the same text will be sent through the EmPy
processor multiple times. Example::
This construct allows self-evaluation:
@:2 + 2:this will get replaced with 4:
**'@{ STATEMENTS }'** -- Execute a (potentially compound)
statement; statements have no return value, so the expansion is
not replaced with anything. Multiple statements can either be
separated on different lines, or with semicolons; indentation is
significant, just as in normal Python code. Statements,
however, can have side effects, including printing; output to
'sys.stdout' (explicitly or via a 'print' statement) is
collected by the interpreter and sent to the output (unless this
behavior is suppressed with the -n option). The usual Python
indentation rules must be followed, although if the statement
consists of only one statement, leading and trailing whitespace
is ignored (*e.g.*, '@{ print time.time() }' is equivalent to
'@{print time.time()}'). Example::
@{x = 123}
@{a = 1; b = 2}
@{print time.time()}
@# Note that extra newlines will appear above because of the
@# newlines trailing the close braces. To suppress them
@# use a @ before the newline:
@{
for i in range(10):
print "i is %d" % i
}@
@{print "Welcome to EmPy."}@
**'@% KEY (WHITESPACE VALUE)_opt NEWLINE'** -- Declare a
significator. Significators consume the whole line (including
the trailing newline), and consist of a key string containing no
whitespace, and than optional value prefixed by whitespace. The
key may not start with or contain internal whitespace, but the
value may; preceding or following whitespace in the value is
stripped. Significators are totally optional, and are intended
to be used for easy external (that is, outside of EmPy)
identification when used in large scale environments with many
EmPy files to be processed. The purpose of significators is to
provide identification information about each file in a special,
easy-to-parse form so that external programs can process the
significators and build databases, independently of EmPy.
Inside of EmPy, when a significator is encountered, its key,
value pair is translated into a simple assignment of the form
'__KEY__ = VALUE' , where "__KEY__" is the key string with two
underscores on either side and "VALUE" is a Python expression.
Example::
@%title "Gravitation"
@%author "Misner", "Thorne", "Wheeler"
@%publisher "W.H. Freeman and Company"
@%pages 1279
@%keywords 'physics', 'gravity', 'Einstein', 'relativity'
@%copyright 1970, 1971
**'@< CONTENTS >'** -- Invoke a custom markup. The custom markup
is a special markup reserved for use by the user; it has no
prescribed meaning on its own. If 'contents' is a string
representing what appears in between the angle brackets, then
expanding this markup is equivalent to
'empy.invokeCallback(contents)'. See the "Custom markup"
section for more information.
Control
EmPy version 3 and above includes the ability to direct
conditional and repeated expansion of blocks of EmPy code with
control markups (the obsolescent "substitution" markups are
unavailable as of version 3.0). Control markups have analogs to
control flow structures in Python such as 'if/elif/else', 'for', and
'while'. Control markups are set off with the '@[...]' notation.
Control markups are designed to be used in precisely the same way
that their internal Python analogues are used, except that the
control markups are intended to be used where there is much more
markup than control structure.
Some control markups are considered "primary," (*e.g.*, 'if',
'for', 'while') as they begin a control markup. Others are
considered "secondary," since they can only appear inside control
flow markups delineated by primary markups (*e.g.*, 'elif',
'else', 'continue', 'break').
Since EmPy, unlike Python, cannot use indentation to determine
where control structures begin and end, all primary control
markups *must* be followed by a corresponding terminating control
markup::
@[PRIMARY ...]...@[end PRIMARY]
(where 'PRIMARY' represents one of the primary keywords). The end
markup is mandatory, as is the space between the 'end' and the
starting keyword. For instance::
@# If `person' is alive, show their age.
@person.name is @
@[if person.isAlive]@person.age@[else]dead@[end if].
All primary markups must be terminated in this way, and the
keyword appearing in the appropriate 'end' markup must match the
primary markup it corresponds to; if either of these conditions
are not satisfied, the result is a parse error. Everything
between the starting control flow marker ('@[PRIMARY ...]') and
the ending marker ('@[end PRIMARY]') -- including other markups,
even control markups -- is considered part of the markup. Control
markups can be nested::
@# Print all non-false elements on separate lines.
@[for elem in elements]@[if elem]@elem@\n@[end if]@[end for]
Three major types of primary control markups are available:
conditional (*e.g.*, 'if', 'try'), looping (*e.g.*, 'for',
'while'), and definitional (*e.g.*, 'def', discussed below).
Conditional control markups conditionally expand their contents,
whereas looping control markups repeatedly expand their contents.
The third type, definitional markups, will define new objects in
the globals relating to their contents. Conditional and looping
markups also differ in one substantial respect: Looping constructs
support '@[continue]' and '@[break]' markups which, like their
Python equivalents, continue with the next iteration or break out
of the innermost looping construct, respectively ('@[continue]'
and '@[break]' markups have no meaning inside conditional markups
and are an error). Also like their Python equivalents,
'@[continue]' and '@[break]' may appear inside nested markups, so
long as they ultimately are contained by at least one looping
control markup::
@# Walk a long a linked list, printing each element.
@[while 1]@
@node
@{node = node.next}@
@[if not node]@[break]@[end if]@
@[end while]
The provided markups are designed to mimic the internal Python
control structures as closely as possible. The supported control
markups are (the phrases in all uppercase are intended to signify
user-selectable patterns)::
@[if CONDITION1]...@[elif CONDITION2]...@[else]...@[end if]
@[try]...@[except ...]...@[except ...]...@[end try]
@[try]...@[finally]...@[end try]
@[for VARIABLE in SEQUENCE]...@[else]...@[end for]
@[while CONDITION]...@[else]...@[end while]
@[def SIGNATURE]...@[end def]
All recognizable forms behave like their Python equivalents; 'if'
can contain multiple 'elif' secondary markups within it; the
'else' markups are optional (but must appear at the end), the
'try' form with the 'except' clause can contain multiple ones
which are handled in sequence, the 'try' form can either contain
one or more 'except' clauses or one 'finally' clause (but not
both), and the 'for' and 'while' structures can contain 'continue'
or 'break' clauses internally (even if contained within other
markups).
The third type of primary control markup is "definitional," in
that they create objects in the globals for later use (*e.g.*,
'def'). This allows the definition of a callable object which,
when called, will expand the contained markup (which can in turn,
of course, contain further markups). The argument to the markup
can be any legal Python function signature::
@[def f(x, y, z=2, *args, **keywords)]...@[end def]
would define a function in the globals named 'f' that takes the
given arguments. A macro markup of the form '@[def
SIGNATURE]CODE@[end def]' is equivalent to the Python code::
def SIGNATURE:
r"""CODE""" # so it is a doc string
empy.expand(r"""CODE""", locals())
That is, it creates a Python function with the same name and
function arguments, whose docstring is the contents of the EmPy
markup that will be expanded when called. And, when called, it
will expand those contents, with the locals passed in.
Unicode support
EmPy version 3.1 and above includes intrinsic Unicode support.
EmPy's Unicode support defers to Python's internal Unicode
support, available in Python 2.0 and up, in order to allow
seamless and transparent translation of different encodings to the
native Python Unicode format.
Knowledge of Python's Unicode support is expected, although not
completely required, to gain full benefit of EmPy's Unicode
features. To enable Unicode support, start EmPy with the
-u/--unicode option. EmPy will then transparently encode from the
input stream, process markups internally with native Unicode, and
then decode transparently to the output stream.
By default, Python sets 'sys.stdin' and 'sys.stdout' with a
default encoding which is accessible via
'sys.getdefaultencoding()'; encodings are represented by string
names. These streams have encodings set by the system and
*cannot* be changed.
However, encodings for newly created files (files to be read when
specified on the command line, and/or files to be written when
used with the -o and -a arguments) can be specified for EmPy via
command line options. The --unicode-encoding option
simultaneously indicates the encoding to be used for both input
and output, whereas the --unicode-input-encoding and
--unicode-output-encoding options can each be used to specify
different encodings for both input and output. (If an encoding is
not explicitly indicated, it resorts to the system default in
'sys.getdefaultencoding()', which is locale dependent.)
Python's Unicode implementation has the concept of error handlers,
registered with the 'codecs' module, which can be specified to
determine what action should take place if input cannot be decoded
into Unicode, or Unicode cannot be encoded into output. EmPy uses
these same "errors," as they are called, and can be specified via
command line options. The three most common error handlers are:
'ignore', where invalid sequences are simply ignored; 'replace',
where invalid sequences are replaced with an encoding-specific
indicator, usually a question mark; and 'strict', where invalid
sequences raise an error. The --unicode-errors command line
option specifies the same error handler to be used for both input
and output, and the --unicode-input-errors and
--unicode-output-errors options can specify different error
handlers for input and output. If an error handler is not
explicitly specified, the 'strict' handler (which will raise
errors) is used.
Remember, to specify input encodings or errors that will take
effect, one cannot take input from 'sys.stdin' and must explicitly
specify an EmPy file to process on the command line. Similarly,
for output encodings or errors, 'sys.stdout' cannot be used and an
explicit output file must be specified with the -o or -a options.
It is perfectly valid to enable the Unicode subsystem (-u option)
while using 'sys.stdin' and 'sys.stdout', but the encodings and
errors of these preexisting streams cannot be changed.
Combined with the --no-prefix option, which disables all markup
processing, EmPy can act merely as an encoding translator, relying
on Python's Unicode facilities::
em.py --no-prefix \
--unicode-input-encoding=utf-8 \
--unicode-output-encoding=latin-1 \
-o filename.Latin-1 filename.UTF-8
Significators
Significators, introduced in EmPy version 1.2, are intended to
represent special assignment in a form that is easy to externally
parse. For instance, if one has a system that contains many EmPy
files, each of which has its own title, one could use a 'title'
significator in each file and use a simple regular expression to
find this significator in each file and organize a database of the
EmPy files to be built. This is an easier proposition than, for
instance, attempting to grep for a normal Python assignment
(inside a '@{...}' expansion) of the desired variable.
Significators look like the following::
@%KEY VALUE
including the trailing newline, where "key" is a name and "value"
is a Python expression, and are separated by any whitespace. This
is equivalent to the following Python code::
__KEY__ = VALUE
That is to say, a significator key translates to a Python variable
consisting of that key surrounded by double underscores on either
side. The value may contain spaces, but the key may not. So::
@%title "All Roads Lead to Rome"
translates to the Python code::
__title__ = "All Roads Lead to Rome"
but obviously in a way that easier to detect externally than if
this Python code were to appear somewhere in an expansion. Since
significator keys are surrounded by double underscores,
significator keys can be any sequence of alphanumeric and
underscore characters; choosing '123' is perfectly valid for a
significator (although straight), since it maps to the name
'__123__' which is a legal Python identifier.
Note the value can be any Python expression. The value can be
omitted; if missing, it is treated as 'None'.
Significators are completely optional; it is completely legal for
a EmPy file or files to be processed without containing any
significators. Significators can appear anywhere within a file
outside of other markups, but typically they are placed near the
top of the file to make them easy to spot and edit by humans.
A regular expression string designed to match significators (with
the default prefix) is available as 'empy.SIGNIFICATOR_RE_STRING',
and also is a toplevel definition in the 'em' module itself.
Diversions
EmPy supports an extended form of diversions, which are a
mechanism for deferring and recalling output on demand, similar to
the functionality included in m4. Multiple "streams" of output
can be diverted (deferred) and undiverted (recalled) in this
manner. A diversion is identified with a name, which is any
immutable object such an integer or string. When recalled,
diverted code is *not* resent through the EmPy interpreter
(although a filter could be set up to do this).
By default, no diversions take place. When no diversion is in
effect, processing output goes directly to the specified output
file. This state can be explicitly requested at any time by
calling the 'empy.stopDiverting' function. It is always legal to
call this function.
When diverted, however, output goes to a deferred location which
can then be recalled later. Output is diverted with the
'empy.startDiversion' function, which takes an argument that is
the name of the diversion. If there is no diversion by that name,
a new diversion is created and output will be sent to that
diversion; if the diversion already exists, output will be
appended to that preexisting diversion.
Output send to diversions can be recalled in two ways. The first
is through the 'empy.playDiversion' function, which takes the
name of the diversion as an argument. This recalls the named
diversion, sends it to the output, and then erases that
diversion. A variant of this behavior is the
'empy.replayDiversion', which recalls the named diversion but does
not eliminate it afterwards; 'empy.replayDiversion' can be
repeatedly called with the same diversion name, and will replay
that diversion repeatedly. 'empy.createDiversion' create a
diversion without actually diverting to it, for cases where you
want to make sure a diversion exists but do not yet want to send
anything to it.
The diversion object itself can be retrieved with
'empy.retrieveDiversion'. Diversions act as writable
file-objects, supporting the usual 'write', 'writelines', 'flush',
and 'close' methods. The data that has been diverted to them can
be retrieved in one of two ways; either through the 'asString'
method, which returns the entire contents of the diversion as a
single strong, or through the 'asFile' method, which returns the
contents of the diversion as a readable (not writable) file-like
object.
Diversions can also be explicitly deleted without recalling them
with the 'empy.purgeDiversion' function, which takes the desired
diversion name as an argument.
Additionally there are three functions which will apply the above
operations to all existing diversions: 'empy.playAllDiversions',
'empy.replayAllDiversions', and 'empy.purgeAllDiversions'. All
three will do the equivalent of a 'empy.stopDiverting' call before
they do their thing.
The name of the current diversion can be requested with the
'empy.getCurrentDiversion' function; also, the names of all
existing diversions (in sorted order) can be retrieved with
'empy.getAllDiversions'.
When all processing is finished, the equivalent of a call to
'empy.playAllDiversions' is done.
Filters
EmPy also supports dynamic filters, introduced in version 1.3.
Filters are put in place right "before" the final output file, and
so are only invoked after all other processing has taken place
(including interpreting and diverting). Filters take input, remap
it, and then send it to the output.
The current filter can be retrieved with the 'empy.getFilter'
function. The filter can be cleared (reset to no filter) with
'empy.resetFilter' and a special "null filter" which does not send
any output at all can be installed with 'empy.nullFilter'. A
custom filter can be set with the 'empy.setFilter' function; for
convenience, specialized shortcuts for filters preexist and can be
used in lieu of actual 'empy.Filter' instances for the
'empy.setFilter' or 'empy.attachFilter' argument:
- 'None' is a special filter meaning "no filter"; when installed,
no filtering whatsoever will take place. 'empy.setFilter(None)'
is equivalent to 'empy.resetFilter()'.
- '0' (or any other numeric constant equal to zero) is another
special filter that represents the null filter; when installed,
no output will ever be sent to the filter's sink.
- A filter specified as a function (or lambda) is expected to take
one string argument and return one string argument; this filter
will execute the function on any input and use the return value
as output.
- A filter that is a string is a 256-character table is
substituted with the result of a call to 'string.translate'
using that table.
- A filter can be an instance of a subclass of 'empy.Filter'.
This is the most general form of filter. (In actuality, it can
be any object that exhibits a 'Filter' interface, which would
include the normal file-like 'write', 'flush', and 'close'
methods, as well as 'next', 'attach', and 'detach' methods for
filter-specific behavior.)
- Finally, the argument to 'empy.setFilter' can be a Python list
consisting of one or more of the above objects. In that case,
those filters are chained together in the order they appear in
the list. An empty list is the equivalent of 'None'; all
filters will be uninstalled.
Filters are, at their core, simply file-like objects (minimally
supporting 'write', 'flush', and 'close' methods that behave in
the usual way) which, after performing whatever processing they
need to do, send their work to the next file-like object or filter
in line, called that filter's "sink." That is to say, filters can
be "chained" together; the action of each filter takes place in
sequence, with the output of one filter being the input of the
next. Additionally, filters support a '_flush' method (note the
leading underscore) which will always flush the filter's
underlying sink; this method should be not overridden.
Filters also support three additional methods, not part of the
traditional file interface: 'attach', which takes as an argument a
file-like object (perhaps another filter) and sets that as the
filter's "sink" -- that is, the next filter/file-like object in
line. 'detach' (which takes no arguments) is another method which
flushes the filter and removes its sink, leaving it isolated.
Finally, 'next' is an accessor method which returns the filter's
sink -- or 'None', if the filter does not yet have a sink
attached.
To create your own filter, you can create an object which supports
the above described interface, or simply derive from the
'empy.Filter' class and override its 'write' and possibly 'flush'
methods. You can chain filters together by passing them as
elements in a list to the 'empy.setFilter' function, or you can
chain them together manually with the 'attach' method::
firstFilter.attach(secondFilter)
empy.setFilter(firstFilter)
or just let EmPy do the chaining for you::
empy.setFilter([firstFilter, secondFilter])
In either case, EmPy will walk the filter chain and find the end
and then hook that into the appropriate interpreter stream; you
need not do this manually. The function 'empy.attachFilter' can
be used to attach a single filter (or shortcut, as above) to the
end of a currently existing chain. Note that unlike its cousin
'empy.setFilter', one cannot pass a sequence of filters (or filter
shortcuts) to 'empy.attachFilter'. (If there is no existing
filter chain installed, 'empy.attachFilter' will behave the same
as 'empy.setFilter'.)
Subclasses of 'empy.Filter' are already provided with the above
null, function, and string functionality described above; they are
'NullFilter', 'FunctionFilter', and 'StringFilter', respectively.
In addition, a filter which supports buffering, 'BufferedFilter',
is provided. Several variants are included: 'SizeBufferedFilter',
a filter which buffers into fixed-sized chunks,
'LineBufferedFilter', a filter which buffers by lines, and
'MaximallyBufferedFilter', a filter which completely buffers its
input.
Hooks
The EmPy system allows for the registry of hooks with a running
EmPy interpreter. Originally introduced in version 2.0 and much
improved in 3.2, hooks are objects, registered with an
interpreter, whose methods represent specific callbacks. Any
number of hook objects can be registered with an interpreter, and
when a callback is invoked, the associated method on each one of
those hook objects will be called by the interpreter in sequence.
Hooks are simply instances, nominally derived from the 'empy.Hook'
class. The 'empy.Hook' class itself defines a series of methods,
with the expected arguments, which would be called by a running
EmPy interpreter. This scenario, much improved from the prior
implementation in 2.0, allows hooks to keep state and have more
direct access to the interpreter they are running in (the
'empy.Hook' instance contains an 'interpreter' attribute).
To use a hook, derive a class from 'empy.Hook' and override the
desired methods (with the same signatures as they appear in the
base class). Create an instance of that subclass, and then
register it with a running interpreter with the 'empy.addHook'
function. (This same hook instance can be removed with the
'empy.removeHook' function.)
More than one hook instance can be registered with an interpreter;
in such a case, the appropriate methods are invoked on each
instance in the order in which they were registered. To adjust
this behavior, an optional 'prepend' argument to the
'empy.addHook' function can be used dictate that the new hook
should placed at the *beginning* of the sequence of hooks, rather
than at the end (which is the default).
All hooks can be enabled and disabled entirely for a given
interpreter; this is done with the 'empy.enableHooks' and
'empy.disableHooks' functions. By default hooks are enabled, but
obviously if no hooks have been registered no hook callbacks will
be made. Whether hooks are enabled or disabled can be determined
by calling 'empy.areHooksEnabled'. To get a (copy of) the list of
registered hooks, call 'empy.getHooks'. Finally, to invoke a hook
manually, use 'empy.invokeHook'.
For a list of supported hook callbacks, see the 'empy.Hook' class
definition.
As a practical example, this sample Python code would print a
pound sign followed by the name of every file that is included
with 'empy.include'::
class IncludeHook(empy.Hook):
def beforeInclude(self, name, file, locals):
print "# %s" % name
empy.addHook(IncludeHook())
Custom markup
Since version 3.2.1, the markup '@<...>' is reserved for
user-defined use. Unlike the other markups, this markup has no
specified meaning on its own, and can be provided a meaning by the
user. This meaning is provided with the use of a "custom
callback," or just "callback," which can be set, queried, or reset
using the pseudomodule function.
The custom callback is a callable object which, when invoked, is
passed a single argument: a string representing the contents of
what was found inside the custom markup '@<...>'.
To register a callback, call 'empy.registerCallback'. To remove
one, call 'empy.deregisterCallback'. To retrieve the callback (if
any) registered with the interpreter, use 'empy.getCallback'.
Finally, to invoke the callback just as if the custom markup were
encountered, call 'empy.invokeCallback'. For instance, '@<This
text>' would be equivalent to the call '@empy.invokeCallback("This
text")'.
By default, to invoke a callback (either explicitly with
'empy.invokeCallback' or by processing a '@<...>' custom markup)
when no callback has been registered is an error. This behavior
can be changed with the 'CALLBACK_OPT' option, or the
--no-callback-error command line option.
Pseudomodule
The 'empy' pseudomodule is available only in an operating EmPy
system. (The name of the module, by default 'empy', can be
changed with the -m option or the 'EMPY_PSEUDO' environment
variable). It is called a pseudomodule because it is not actually
a module, but rather exports a module-like interface. In fact,
the pseudmodule is actually the same internal object as the
interpreter itself.
The pseudomodule contains the following functions and objects (and
their signatures, with a suffixed 'opt' indicating an optional
argument):
First, basic identification:
**'VERSION'** -- A constant variable which contains a
string representation of the EmPy version.
**'SIGNIFICATOR_RE_STRING'** -- A constant variable representing a
regular expression string (using the default prefix) that can be
used to find significators in EmPy code.
**'SIGNIFICATOR_RE_SUFFIX'** -- The portion of the significator
regular expression string excluding the prefix, so that those
using non-standard prefix can build their own custom regular
expression string with 'myPrefix + empy.SIGNIFICATOR_RE_SUFFIX'.
**'interpreter'** -- The instance of the interpreter that is
currently being used to perform execution. *Note:* This is now
obsolete; the pseudomodule is itself the interpreter. Instead
of using 'empy.interpreter', simply use 'empy'.
**'argv'** -- A list consisting of the name of the primary EmPy
script and its command line arguments, in analogue to the
'sys.argv' list.
**'args'** -- A list of the command line arguments following the
primary EmPy script; this is equivalent to 'empy.argv[1:]'.
**'identify() -> string, integer'** -- Retrieve identification
information about the current parsing context. Returns a
2-tuple consisting of a filename and a line number; if the file
is something other than from a physical file (*e.g.*, an
explicit expansion with 'empy.expand', a file-like object within
Python, or via the -E or -F command line options), a string
representation is presented surrounded by angle brackets. Note
that the context only applies to the *EmPy* context, not the
Python context.
**'atExit(callable)'** -- Register a callable object (such as a
function) taking no arguments which will be called at the end of
a normal shutdown. Callable objects registered in this way are
called in the reverse order in which they are added, so the
first callable registered with 'empy.atExit' is the last one to
be called. Note that although the functionality is related to
hooks, 'empy.atExit' does no work via the hook mechanism, and
you are guaranteed that the interpreter and stdout will be in a
consistent state when the callable is invoked.
Context manipulation:
**'pushContext(name_opt, line_opt)'** -- Create a new context with
the given name and line and push it on the stack.
**'popContext()'** -- Pop the top context and dispose of it.
**'setContextName(name)'** -- Manually set the name of the current
context.
**'setContextLine(line)'** -- Manually set the line number of the
current context; line must be a numeric value. Note that
afterward the line number will increment by one for each newline
that is encountered, as before.
Globals manipulation:
**'getGlobals()'** -- Retrieve the globals dictionary for this
interpreter. Unlike when calling 'globals()' in Python, this
dictionary *can* be manipulated and you *can* expect changes you
make to it to be reflected in the interpreter that holds it.
**'setGlobals(globals)'** -- Reseat the globals dictionary
associated with this interpreter to the provided mapping type.
**'updateGlobals(globals)'** -- Merge the given dictionary into
this interpreter's globals.
**'clearGlobals(globals_opt)'** -- Clear out the globals
(restoring, of course, the 'empy' pseudomodule). Optionally,
instead of starting with a refresh dictionary, use the
dictionary provided.
**'saveGlobals(deep=True)'** -- Save a copy of the globals onto an
internal history stack from which it can be restored later. The
optional 'deep' argument indicates whether or not the copying
should be a deep copy (default) or a shallow one. Copying is
done with 'copy.deepcopy' or 'copy.copy', respectively.
**'restoreGlobals(destructive=True)'** -- Restore the most
recently saved globals from the history stack to as the current
globals for this instance. The optional 'destructive' argument
indicates whether or not the restore should remove the restored
globals from the history stack (default), or whether it should
be left there for subsequent restores.
Types:
**'Interpreter'** -- The actual interpreter class.
The following functions allow direct execution; optional 'locals'
arguments, if specified, are treated as the locals dictionary in
evaluation and execution:
**'defined(name, locals_opt)'** -- Return true if the given name
is defined either in the (optional) locals or the interpreter
globals; return false otherwise.
**'evaluate(expression, locals_opt)'** -- Evaluate the given
expression.
**'serialize(expression, locals_opt)'** -- Serialize the
expression, just as the interpreter would: If it is not None,
convert it to a string with the 'str' builtin function, and then
write out the result. If it evaluates to None, do nothing.
**'execute(statements, locals_opt)'** -- Execute the given
statement(s).
**'single(source, locals_opt)'** -- Interpret the "single" source
code, just as the Python interactive interpreter would.
**'import_(name, locals_opt)'** -- Import a module.
**'atomic(name, value, locals_opt)'** -- Perform a single, atomic
assignment. In this case name is the string denoating the name
of the (single) variable to be assigned to, and value is a
Python object which the name is to be bound to.
**'assign(name, value, locals_opt)'** -- Perform general
assignment. This decays to atomic assignment (above) in the
normal case, but supports "tuple unpacking" in the sense that if
name string contains commas, it is treated as a sequence of
names and memberwise assignment with each member of the value
(still a Python object, but which must be a sequence). This
function will raise a 'TypeError' or 'ValueError' just like
Python would if tuple unpacking is not possible (that is, if the
value is not a sequence or is of an incompatible length,
respectively). This only supports the assignment of Python
identifiers, not arbitrary Python lvalues.
**'significate(key, value_opt, locals_opt)'** -- Do a manual
signification. If 'value' is not specified, it is treated as
'None'.
The following functions relate to source manipulation:
**'include(file_or_filename, locals_opt)'** -- Include another
EmPy file, by processing it in place. The argument can either
be a filename (which is then opened with 'open' in text mode) or
a file object, which is used as is. Once the included file is
processed, processing of the current file continues. Includes
can be nested. The call also takes an optional locals
dictionary which will be passed into the evaluation function.
**'expand(string, locals_opt)' -> string** -- Explicitly invoke
the EmPy parsing system to process the given string and return
its expansion. This allows multiple levels of expansion,
*e.g.*, '@(empy.expand("@(2 + 2)"))'. The call also takes an
optional locals dictionary which will be passed into the
evaluation function. This is necessary when text is being
expanded inside a function definition and it is desired that the
function arguments (or just plain local variables) are available
to be referenced within the expansion.
**'quote(string) -> string'** -- The inverse process of
'empy.expand', this will take a string and return a new string
that, when expanded, would expand to the original string. In
practice, this means that appearances of the prefix character
are doubled, except when they appear inside a string literal.
**'escape(string, more_opt) -> string'** -- Given a string, quote
the nonprintable characters contained within it with EmPy
escapes. The optional 'more' argument specifies additional
characters that should be escaped.
**'flush()'** -- Do an explicit flush on the underlying stream.
**'string(string, name_opt, locals_opt)'** -- Explicitly process a
string-like object. This differs from 'empy.expand' in that the
string is directly processed into the EmPy system, rather than
being evaluated in an isolated context and then returned as a
string.
Changing the behavior of the pseudomodule itself:
**'flatten(keys_opt)'** -- Perform the equivalent of 'from empy
import ...' in code (which is not directly possible because
'empy' is a pseudomodule). If keys is omitted, it is taken as
being everything in the 'empy' pseudomodule. Each of the
elements of this pseudomodule is flattened into the globals
namespace; after a call to 'empy.flatten', they can be referred
to simple as globals, *e.g.*, '@divert(3)' instead of
'@empy.divert(3)'. If any preexisting variables are bound to
these names, they are silently overridden. Doing this is
tantamount to declaring an 'from ... import ...' which is often
considered bad form in Python.
Prefix-related functions:
**'getPrefix() -> char'** -- Return the current prefix.
**'setPrefix(char)'** -- Set a new prefix. Immediately after this
call finishes, the prefix will be changed. Changing the prefix
affects only the current interpreter; any other created
interpreters are unaffected. Setting the prefix to None or the
null string means that no further markups will be processed,
equivalent to specifying the --no-prefix command line argument.
Diversions:
**'stopDiverting()'** -- Any diversions that are currently taking
place are stopped; thereafter, output will go directly to the
output file as normal. It is never illegal to call this
function.
**'createDiversion(name)'** -- Create a diversion, but do not
begin diverting to it. This is the equivalent of starting a
diversion and then immediately stopping diversion; it is used in
cases where you want to make sure that a diversion will exist
for future replaying but may be empty.
**'startDiversion(name)'** -- Start diverting to the specified
diversion name. If such a diversion does not already exist, it
is created; if it does, then additional material will be
appended to the preexisting diversions.
**'playDiversion(name)'** -- Recall the specified diversion and
then purge it. The provided diversion name must exist.
**'replayDiversion(name)'** -- Recall the specified diversion
without purging it. The provided diversion name must exist.
**'purgeDiversion(name)'** -- Purge the specified diversion
without recalling it. The provided diversion name must exist.
**'playAllDiversions()'** -- Play (and purge) all existing
diversions in the sorted order of their names. This call does
an implicit 'empy.stopDiverting' before executing.
**'replayAllDiversions()'** -- Replay (without purging) all
existing diversions in the sorted order of their names. This
call does an implicit 'empy.stopDiverting' before executing.
**'purgeAllDiversions()'** -- Purge all existing diversions
without recalling them. This call does an implicit
'empy.stopDiverting' before executing.
**'getCurrentDiversion() -> diversion'** -- Return the name of the
current diversion.
**'getAllDiversions() -> sequence'** -- Return a sorted list of
all existing diversions.
Filters:
**'getFilter() -> filter'** -- Retrieve the current filter.
'None' indicates no filter is installed.
**'resetFilter()'** -- Reset the filter so that no filtering is
done.
**'nullFilter()'** -- Install a special null filter, one which
consumes all text and never sends any text to the output.
**'setFilter(shortcut)'** -- Install a new filter. A filter is
'None' or an empty sequence representing no filter, or '0' for a
null filter, a function for a function filter, a string for a
string filter, or an instance of 'empy.Filter' (or a workalike
object). If filter is a list of the above things, they will be
chained together manually; if it is only one, it will be
presumed to be solitary or to have already been manually chained
together. See the "Filters" section for more information.
**'attachFilter(shortcut)'** -- Attach a single filter (sequences
are not allowed here) to the end of a currently existing filter
chain, or if there is no current chain, install it as
'empy.setFilter' would. As with 'empy.setFilter', the shortcut
versions of filters are also allowed here.
Hooks:
**'areHooksEnabled()'** -- Return whether or not hooks are
presently enabled.
**'enableHooks()'** -- Enable invocation of hooks. By default
hooks are enabled.
**'disableHooks()'** -- Disable invocation of hooks. Hooks can
still be added, removed, and queried, but invocation of hooks
will not occur (even explicit invocation with
'empy.invokeHook').
**'getHooks()'** -- Get a (copy of the) list of the hooks
currently registered.
**'clearHooks()'** -- Clear all the hooks registered with this
interpreter.
**'addHook(hook, prepend_opt)'** -- Add this hook to the hooks
associated with this interpreter. By default, the hook is
appended to the end of the existing hooks, if any; if the
optional insert argument is present and true, it will be
prepended to the list instead.
**'removeHook(hook)'** -- Remove this hook from the hooks
associated with this interpreter.
**'invokeHook(_name, ...)'** -- Manually invoke a hook method.
The remaining arguments are treated as keyword arguments and the
resulting dictionary is passed in as the second argument to the
hooks.
Custom markup callback:
**'getCallback() -> callback'** -- Retrieve the current callback
associated with this interpreter, or 'None' if it does not yet
have one.
**'registerCallback(callback)'** -- Register a callback to be
called whenever a custom markup ('@<...>') is encountered. When
encountered, 'invokeCallback' is called.
**'deregisterCallback()'** -- Clear any callback previously
registered with the interpreter for being called when a custom
markup is encountered.
**'invokeCallback(contents)'** -- Invoke a custom callback. This
function is called whenever a custom markup ('@<...>') is
encountered. It in turn calls the registered callback, with a
single argument, 'contents', which is a string representing of
the contents of the custom markup.
Invocation
Basic invocation involves running the interpreter on an EmPy file
and some optional arguments. If no file are specified, or the
file is named '-', EmPy takes its input from stdin. One can
suppress option evaluation (to, say, specify a file that begins
with a dash) by using the canonical '--' option.
**'-h'/'--help'** -- Print usage and exit.
**'-H'/'--extended-help'** -- Print extended usage and exit.
Extended usage includes a rundown of all the legal expansions,
escape sequences, pseudomodule contents, used hooks, and
supported environment variables.
**'-v'/'--verbose'** -- The EmPy system will print all manner of
details about what it is doing and what it is processing to
stderr.
**'-V'/'--version'** -- Print version and exit.
**'-a'/'--append' (filename)** -- Open the specified file for
append instead of using stdout.
**'-b'/'--buffered-output'** -- Fully buffer processing output,
including the file open itself. This is helpful when, should an
error occur, you wish that no output file be generated at all
(for instance, when using EmPy in conjunction with make). When
specified, either the -o or -a options must be specified, and
the -b option must precede them. This can also be specified
through the existence of the 'EMPY_BUFFERED_OUTPUT' environment
variable.
**'-f'/'--flatten'** -- Before processing, move the contents of
the 'empy' pseudomodule into the globals, just as if
'empy.flatten()' were executed immediately after starting the
interpreter. That is, *e.g.*, 'empy.include' can be referred to
simply as 'include' when this flag is specified on the command
line. This can also be specified through the existence of the
'EMPY_FLATTEN' environment variable.
**'-i'/'--interactive'** -- After the main EmPy file has been
processed, the state of the interpreter is left intact and
further processing is done from stdin. This is analogous to the
Python interpreter's -i option, which allows interactive
inspection of the state of the system after a main module is
executed. This behaves as expected when the main file is stdin
itself. This can also be specified through the existence of the
'EMPY_INTERACTIVE' environment variable.
**'-k'/'--suppress-errors'** -- Normally when an error is
encountered, information about its location is printed and the
EmPy interpreter exits. With this option, when an error is
encountered (except for keyboard interrupts), processing stops
and the interpreter enters interactive mode, so the state of
affairs can be assessed. This is also helpful, for instance,
when experimenting with EmPy in an interactive manner. -k
implies -i.
**'-n'/'--no-override-stdout'** -- Do not override 'sys.stdout'
with a proxy object which the EmPy system interacts with. If
suppressed, this means that side effect printing will not be
captured and routed through the EmPy system. However, if this
option is specified, EmPy can support multithreading.
**'-o'/'--output' (filename)** -- Open the specified file for
output instead of using stdout. If a file with that name
already exists it is overwritten.
**'-p'/'--prefix' (prefix)** -- Change the prefix used to detect
expansions. The argument is the one-character string that will
be used as the prefix. Note that whatever it is changed to, the
way to represent the prefix literally is to double it, so if '$'
is the prefix, a literal dollar sign is represented with '$$'.
Note that if the prefix is changed to one of the secondary
characters (those that immediately follow the prefix to indicate
the type of action EmPy should take), it will not be possible to
represent literal prefix characters by doubling them (*e.g.*, if
the prefix were inadvisedly changed to '#' then '##' would
already have to represent a comment, so '##' could not represent
a literal '#'). This can also be specified through the
'EMPY_PREFIX' environment variable.
**'-r'/'--raw-errors'** -- Normally, EmPy catches Python
exceptions and prints them alongside an error notation
indicating the EmPy context in which it occurred. This option
causes EmPy to display the full Python traceback; this is
sometimes helpful for debugging. This can also be specified
through the existence of the 'EMPY_RAW_ERRORS' environment
variable.
**'-u'/'--unicode'** -- Enable the Unicode subsystem. This option
only need be present if you wish to enable the Unicode subsystem
with the defaults; any other Unicode-related option (starting
with --unicode...) will also enable the Unicode subsystem.
**'-D'/'--define' (assignment)** -- Execute a Python assignment of
the form 'variable = expression'. If only a variable name is
provided (*i.e.*, the statement does not contain an '=' sign),
then it is taken as being assigned to None. The -D option is
simply a specialized -E option that special cases the lack of an
assignment operator. Multiple -D options can be specified.
**'-E'/'--execute' (statement)** -- Execute the Python (not EmPy)
statement before processing any files. Multiple -E options can
be specified.
**'-F'/'--execute-file' (filename)** -- Execute the Python (not
EmPy) file before processing any files. This is equivalent to
'-E execfile("filename")' but provides a more readable context.
Multiple -F options can be specified.
**'-I'/'--import' (module)** -- Imports the specified module name
before processing any files. Multiple modules can be specified
by separating them by commas, or by specifying multiple -I
options.
**'-P'/'--preprocess' (filename)** -- Process the EmPy file before
processing the primary EmPy file on the command line.
**'--binary'** -- Treat the file as a binary file, and read in
chunks rather than line by line. In this mode, the "line"
indicator represents the number of bytes read, not the number of
lines processed.
**'--no-prefix'** -- Disable the prefixing system entirely; when
specified, EmPy will not expand any markups. This allows EmPy
to merely act as a Unicode encoding translator..
**'--pause-at-end'** -- If present, then 'raw_input' will be
called at the end of processing. Useful in systems where the
output window would otherwise be closed by the operating
system/window manager immediately after EmPy exited.
**'--relative-path'** -- When present, the path the EmPy script
being invoked is contained in will be prepended to 'sys.path'.
This is analogous to Python's internal handling of 'sys.path'
and scripts. If input is from stdin ('-' for a filename or no
filename is specified), then nothing is added to the path.
**'--no-callback-error'** -- Do not consider it an error if the
custom markup is invoked '@<...>' and there is no callback
function registered for it.
**'--chunk-size' (chunk)** -- Use the specific binary chunk size
rather than the default; implies --binary.
**'--unicode-encoding' (encoding)** -- Specify the Unicode
encoding to be used for both input and output.
**'--unicode-input-encoding' (encoding)** -- Specify the Unicode
encoding to be used for input.
**'--unicode-output-encoding' (encoding)** -- Specify the Unicode
encoding to be used for output.
**'--unicode-input-errors (errors)** -- Specify the Unicode error
handling to be used for input.
**'--unicode-errors (errors)** -- Specify the Unicode error
handling to be used for both input and output.
**'--unicode-output-errors (errors)** -- Specify the Unicode error
handling to be used for output.
Environment variables
EmPy also supports a few environment variables to predefine
certain behaviors. The settings chosen by environment variables
can be overridden via command line arguments. The following
environment variables have meaning to EmPy:
**'EMPY_OPTIONS'** -- If present, the contents of this environment
variable will be treated as options, just as if they were
entered on the command line, *before* the actual command line
arguments are processed. Note that these arguments are *not*
processed by the shell, so quoting, filename globbing, and the
like, will not work.
**'EMPY_PREFIX'** -- If present, the value of this environment
variable represents the prefix that will be used; this is
equivalent to the -p command line option.
**'EMPY_PSEUDO'** -- If present, the value of this environment
variable represents the name of the pseudomodule that will be
incorporated into every running EmPy system; this is equivalent
to the -m command line option.
**'EMPY_FLATTEN'** -- If defined, this is equivalent to including
-f on the command line.
**'EMPY_RAW_ERRORS'** -- If defined, this is equivalent to
including -r on the command line.
**'EMPY_INTERACTIVE'** -- If defined, this is equivalent to
including -i on the command line.
**'EMPY_BUFFERED_OUTPUT'** -- If defined, this is equivalent to
including -b on the command line.
**'EMPY_UNICODE'** -- If defined, this is equivalent to including
-u on the command line.
**'EMPY_UNICODE_INPUT_ENCODING'** -- If present, the value of this
environment variable indicates the name of the Unicode input
encoding to be used. This is equivalent to the
--unicode-input-encoding command line option.
**'EMPY_UNICODE_OUTPUT_ENCODING'** -- If present, the value of
this environment variable indicates the name of the Unicode
output encoding to be used. This is equivalent to the
--unicode-output-encoding command line option.
**'EMPY_UNICODE_INPUT_ERRORS'** -- If present, the value of this
environment variable indicates the name of the error handler to
be used for input. This is equivalent to the
--unicode-input-errors command line option.
**'EMPY_UNICODE_OUTPUT_ERRORS'** -- If present, the value of this
environment variable indicates the name of the error handler to
be used for output. This is equivalent to the
--unicode-output-errors command line option.
Examples and testing EmPy
See the sample EmPy file 'sample.em' which is included with the
distribution. Run EmPy on it by typing something like::
./em.py sample.em
and compare the results and the sample source file side by side.
The sample content is intended to be self-documenting, and even an
introduction to the basic features of EmPy while simultaneously
exercising them.
The file 'sample.bench' is the benchmark output of the sample.
Running the EmPy interpreter on the provided 'sample.em' file
should produce precisely the same results. You can run the
provided test script to see if your EmPy environment is behaving
as expected (presuming a Unix-like operating system)::
./test.sh
By default this will test with the first Python interpreter
available in the path; if you want to test with another
interpreter, you can provide it as the first argument on the
command line, *e.g.*::
./test.sh python2.1
./test.sh /usr/bin/python1.5
./test.sh jython
A more comprehensive test suite and set of real-world examples is
planned for a future version.
Embedding EmPy
For atomic applications, the 'expand' function is provided (the
extra keyword arguments passed in are treated as locals)::
import em
print em.expand("@x + @y is @(x + y).", x=2, y=3)
One can specify a globals dictionary and all the other interpreter
options (below) as well. One can specify a globals dictionary
that will be used if one wants persistence::
import em
g = {}
em.expand("@{x = 10}", g)
print em.expand("x is @x.", g)
The standalone 'expand' function, however, creates and destroys an
'Interpreter' instance each time it is called. For repeated
expansions, this can be expensive. Instead, you will probably
want to use the full-fledged features of embedding. An EmPy
interpreter can be created with as code as simple as::
import em
interpreter = em.Interpreter()
# The following prints the results to stdout:
interpreter.string("@{x = 123}@x\n")
# This expands to the same thing, but puts the results as a
# string in the variable result:
result = interpreter.expand("@{x = 123}@x\n")
# This just prints the value of x directly:
print interpreter.globals['x']
# Process an actual file (and output to stdout):
interpreter.file(open('/path/to/some/file'))
interpreter.shutdown() # this is important; see below
One can capture the output of a run in something other than stdout
by specifying the *output* parameter::
import em, StringIO
output = StringIO.StringIO()
interpreter = em.Interpreter(output=output)
# Do something.
interpreter.file(open('/path/to/some/file'))
interpreter.shutdown() # again, this is important; see below
print output.getvalue() # this is the result from the session
When you are finished with your interpreter, it is important to
call its shutdown method::
interpreter.shutdown()
This will ensure that the interpreter cleans up all its overhead,
entries in the 'sys.stdout' proxy, and so forth. It is usually
advisable that this be used in a try...finally clause::
interpreter = em.Interpreter(...)
try:
...
finally:
interpreter.shutdown()
The 'em.Interpreter' constructor takes the following arguments;
all are optional. Since options may be added in the future, it is
highly recommended that the constructor be invoked via keyword
arguments, rather than assuming their order. The arguments are:
*output* -- The output file which the interpreter will be sending
all its processed data to. This need only be a file-like object;
it need not be an actual file. If omitted, 'sys.__stdout__' is
used.
*argv* -- An argument list analogous to 'sys.argv', consisting of
the script name and zero or more arguments. These are available
to executing interpreters via 'empy.argv' and 'empy.args'. If
omitted, a non-descript script name is used with no arguments.
*prefix* -- The prefix (a single-character string). Defaults to
'@'. It is an error for this to be anything other than one
character.
*pseudo* -- The name (string) of the pseudmodule. Defaults to
'empy'.
*options* -- A dictionary of options that can override the default
behavior of the interpreter. The names of the options are
constant names ending in '_OPT' and their defaults are given in
'Interpreter.DEFAULT_OPTIONS'.
*globals* -- By default, interpreters begin with a pristine
dictionary of globals (except, of course, for the 'empy'
pseudomodule). Specifying this argument will allow the globals
to start with more.
*hooks* -- A sequence of hooks (or 'None' for none) to register
with the interpreter at startup. Hooks can, of course, be added
after the fact, but this allows the hooks to intercept the
'atStartup' event (otherwise, the startup event would already
have occurred by the time new hooks could be registered)..
Many things can be done with EmPy interpreters; for the full
developer documentation, see the generated documentation for the
'em' module.
Interpreter options
The following options (passed in as part of the options dictionary
to the Interpreter constructor) have the following meanings. The
defaults are shown below and are also indicated in an
'Interpreter.DEFAULT_OPTIONS' dictionary.
**'BANGPATH_OPT'** -- Should a bangpath ('#!') as the first line
of an EmPy file be treated as if it were an EmPy comment? Note
that '#!' sequences starting lines or appearing anywhere else in
the file are untouched regardless of the value of this option.
Default: true.
**'BUFFERED_OPT'** -- Should an 'abort' method be called upon
failure? This relates to the fully-buffered option, where all
output can be buffered including the file open; this option only
relates to the interpreter's behavior *after* that proxy file
object has been created. Default: false.
**'RAW_OPT'** -- Should errors be displayed as raw Python errors
(that is, the exception is allowed to propagate through to the
toplevel so that the user gets a standard Python traceback)?
Default: false.
**'EXIT_OPT'** -- Upon an error, should execution continue
(although the interpreter stacks will be purged)? Note that
even in the event this is set, the interpreter will halt upon
receiving a 'KeyboardInterrupt'. Default: true.
**'FLATTEN_OPT'** -- Upon initial startup, should the 'empy'
pseudomodule namespace be flattened, *i.e.*, should
'empy.flatten' be called? Note this option only has an effect
when the interpreter is first created; thereafter it is
ignored. Default: false.
**'OVERRIDE_OPT'** -- Should the 'sys.stdout' object be overridden
with a proxy object? If not, side effect output cannot be
captured by the EmPy system, but EmPy will support
multithreading. Default: true.
**'CALLBACK_OPT'** -- If a callback is invoked when none has yet
been registered, should an error be raised or should the
situation be ignored? Default: true.
Data flow
**input -> interpreter -> diversions -> filters -> output**
Here, in summary, is how data flows through a working EmPy system:
1. Input comes from a source, such an .em file on the command
line, or via an 'empy.include' statement.
2. The interpreter processes this material as it comes in,
expanding EmPy expansions as it goes.
3. After interpretation, data is then sent through the diversion
layer, which may allow it directly through (if no diversion is
in progress) or defer it temporarily. Diversions that are
recalled initiate from this point.
4. Any filters in place are then used to filter the data and
produce filtered data as output.
5. Finally, any material surviving this far is sent to the output
stream. That stream is stdout by default, but can be changed
with the -o or -a options, or may be fully buffered with the -b
option (that is, the output file would not even be opened until
the entire system is finished).
Author's notes
I originally conceived EmPy as a replacement for my "Web
templating system", http://www.alcyone.com/max/info/m4.html which
uses "m4", http://www.seindal.dk/rene/gnu/ (a general
macroprocessing system for Unix).
Most of my Web sites include a variety of m4 files, some of which
are dynamically generated from databases, which are then scanned
by a cataloging tool to organize them hierarchically (so that,
say, a particular m4 file can understand where it is in the
hierarchy, or what the titles of files related to it are without
duplicating information); the results of the catalog are then
written in database form as an m4 file (which every other m4 file
implicitly includes), and then GNU make converts each m4 to an
HTML file by processing it.
As the Web sites got more complicated, the use of m4 (which I had
originally enjoyed for the challenge and abstractness) really
started to become an impediment to serious work; while I am very
knowledgeable about m4 -- having used it for for so many years --
getting even simple things done with it is awkward and difficult.
Worse yet, as I started to use Python more and more over the
years, the cataloging programs which scanned the m4 and built m4
databases were migrated to Python and made almost trivial, but
writing out huge awkward tables of m4 definitions simply to make
them accessible in other m4 scripts started to become almost
farcical -- especially when coupled with the difficulty in getting
simple things done in m4.
It occurred to me what I really wanted was an all-Python solution.
But replacing what used to be the m4 files with standalone Python
programs would result in somewhat awkward programs normally
consisting mostly of unprocessed text punctuated by small portions
where variables and small amounts of code need to be substituted.
Thus the idea was a sort of inverse of a Python interpreter: a
program that normally would just pass text through unmolested, but
when it found a special signifier would execute Python code in a
normal environment. I looked at existing Python templating
systems, and didn't find anything that appealed to me -- I wanted
something where the desired markups were simple and unobtrusive.
After considering between choices of signifiers, I settled on '@'
and EmPy was born.
As I developed the tool, I realized it could have general appeal,
even to those with widely varying problems to solve, provided the
core tool they needed was an interpreter that could embed Python
code inside templated text. As I continue to use the tool, I have
been adding features as unintrusively as possible as I see areas
that can be improved.
A design goal of EmPy is that its feature set should work on
several levels; at each level, if the user does not wish or need
to use features from another level, they are under no obligation
to do so. If you have no need of diversions, for instance, you
are under no obligation to use them. If significators will not
help you organize a set of EmPy scripts globally, then you need
not use them. New features that are being added are whenever
possible transparently backward compatible; if you do not need
them, their introduction should not affect you in any way. The
use of unknown prefix sequences results in errors, guaranteeing
that they are reserved for future use.
Glossary
**control** -- A control markup, used to direct high-level control
flow within an EmPy session. Control markups are expressed with
the '@[...]' notation.
**diversion** -- A process by which output is deferred, and can be
recalled later on demand, multiple times if necessary.
**document** -- The abstraction of an EmPy document as used by a
processor.
**escape** -- A markup designed to expand to a single (usually
non-printable) character, similar to escape sequences in C or
other languages.
**expansion** -- The process of processing EmPy markups and
producing output.
**expression** -- An expression markup represents a Python
expression to be evaluated, and replaced with the 'str' of its
value. Expression markups are expressed with the '@(...)'
notation.
**filter** -- A file-like object which can be chained to other
objects (primarily the final stream) and can buffer, alter, or
manipulate in any way the data sent. Filters can also be
chained together in arbitrary order.
**globals** -- The dictionary (or dictionary-like object) which
resides inside the interpreter and holds the currently-defined
variables.
**hook** -- A callable object that can be registered in a
dictionary, and which will be invoked before, during, or after
certain internal operations, identified by name with a string.
**interpreter** -- The application (or class instance) which
processes EmPy markup.
**markup** -- EmPy substitutions set off with a prefix and
appropriate delimeters.
**output** -- The final destination of the result of processing an
EmPy file.
**prefix** -- The ASCII character used to set off an expansions.
By default, '@'.
**processor** -- An extensible system which processes a group of
EmPy files, usually arranged in a filesystem, and scans them for
significators.
**pseudomodule** -- The module-like object named 'empy' which is
exposed internally inside every EmPy system.
**shortcut** -- A special object which takes the place of an
instance of the 'Filter' class, to represent a special form of
filter. These include 0 for a null filter, a callable (function
or lambda) to represent a callable filter, or a 256-character
string which represents a translation filter.
**significator** -- A special form of an assignment markup in EmPy
which can be easily parsed externally, primarily designed for
representing uniform assignment across a collection of files.
Significators are indicated with the '@%' markup.
**statement** -- A line of code that needs to be executed;
statements do not have return values. In EmPy, statements are
set off with '@{...}'.
Acknowledgements
Questions, suggestions, bug reports, evangelism, and even
complaints from many people have helped make EmPy what it is
today. Some, but by no means all, of these people are (in
alphabetical order by surname):
- Biswapesh Chattopadhyay
- Beni Cherniavsky
- Dr. S. Candelaria de Ram
- Eric Eide
- Dinu Gherman
- Grzegorz Adam Hankiewicz
- Bohdan Kushnir
- Robert Kroeger
- Kouichi Takahashi
- Ville Vainio
Known issues and caveats
- EmPy was primarily intended for static processing of documents,
rather than dynamic use, and hence speed of processing was not
the primary consideration in its design.
- EmPy is not threadsafe by default. This is because of the need
for EmPy to override the 'sys.stdout' file with a proxy object
which can capture effects of 'print' and other spooling to
stdout. This proxy can be suppressed with the -n option, which
will result in EmPy being unable to do anything meaningful with
this output, but will allow EmPy to be threadsafe.
- To function properly, EmPy must override 'sys.stdout' with a
proxy file object, so that it can capture output of side effects
and support diversions for each interpreter instance. It is
important that code executed in an environment *not* rebind
'sys.stdout', although it is perfectly legal to invoke it
explicitly (*e.g.*, '@sys.stdout.write("Hello world\n")'). If
one really needs to access the "true" stdout, then use
'sys.__stdout__' instead (which should also not be rebound).
EmPy uses the standard Python error handlers when exceptions are
raised in EmPy code, which print to 'sys.stderr'.
- Due to Python's curious handling of the 'print' statement --
particularly the form with a trailing comma to suppress the
final newline -- mixing statement expansions using prints inline
with unexpanded text will often result in surprising behavior,
such as extraneous (sometimes even deferred!) spaces. This is a
Python "feature," and occurs in non-EmPy applications as well;
for finer control over output formatting, use 'sys.stdout.write'
or 'empy.interpreter.write' directly.
- The 'empy' "module" exposed through the EmPy interface (*e.g.*,
'@empy') is an artificial module. It cannot be imported with
the 'import' statement (and shouldn't -- it is an artifact of
the EmPy processing system and does not correspond to any
accessible .py file).
- For an EmPy statement expansion all alone on a line, *e.g.*,
'@{a = 1}', note that this will expand to a blank line due to
the newline following the closing curly brace. To suppress this
blank line, use the symmetric convention '@{a = 1}@'.
- When using EmPy with make, note that partial output may be
created before an error occurs; this is a standard caveat when
using make. To avoid this, write to a temporary file and move
when complete, delete the file in case of an error, use the -b
option to fully buffer output (including the open), or (with GNU
make) define a '.DELETE_ON_ERROR' target.
- 'empy.identify' tracks the context of executed *EmPy* code, not
Python code. This means that blocks of code delimited with '@{'
and '}' will identify themselves as appearing on the line at
which the '}' appears, and that pure Python code executed via
the -D, -E and -F command line arguments will show up as all taking
place on line 1. If you're tracking errors and want more
information about the location of the errors from the Python
code, use the -r command line option, which will provide you
with the full Python traceback.
- The conditional form of expression expansion '@(...?...!...)'
allows the use of a colon instead of an exclamation point,
*e.g.*, '@(...?...:...)'. This behavior is supported for
backward compatibility, but is deprecated. Due to an oversight,
the colon was a poor choice since colons can appear legally in
expressions (*e.g.*, dictionary literals or lambda expressions).
- The '@[try]' construct only works with Python exceptions derived
from 'Exception'. It is not able to catch string exceptions.
- The '@[for]' variable specification supports tuples for tuple
unpacking, even recursive tuples. However, it is limited in
that the names included may only be valid Python identifiers,
not arbitrary Python lvalues. Since the internal Python
mechanism is very rarely used for this purpose (*e.g.*, 'for (x,
l[0], q.a) in sequence'), it is not thought to be a significant
limitation.
Wish list
Here are some random ideas for future revisions of EmPy. If any
of these are of particular interest to you, your input would be
appreciated.
- Some real-world examples should really be included for
demonstrating the power and expressiveness of EmPy first-hand.
- More extensive help (rather than a ridiculously long README),
probably inherently using the EmPy system itself for building to
HTML and other formats, thereby acting as a help facility and a
demonstration of the working system.
- A "trivial" mode, where all the EmPy system does is scan for
simple symbols to replace them with evaluations/executions,
rather than having to do the contextual scanning it does now.
This has the down side of being much less configurable and
powerful but the upside of being extremely efficient.
- A "debug" mode, where EmPy prints the contents of everything
it's about to evaluate (probably to stderr) before it does?
- The ability to funnel all code through a configurable 'RExec'
for user-controlled security control. This would probably
involve abstracting the execution functionality outside of the
interpreter. [This suggestion is on hold until the
rexec/Bastion exploits are worked out.]
- Optimized handling of processing would be nice for the
possibility of an Apache module devoted to EmPy processing.
- An EmPy emacs mode.
- An optimization of offloading diversions to files when they
become truly huge. (This is made possible by the abstraction of
the 'Diversion' class.)
- Support for mapping filters (specified by dictionaries).
- Support for some sort of batch processing, where several EmPy
files can be listed at once and all of them evaluated with the
same initial (presumably expensive) environment.
'empy.saveGlobals' and 'empy.restoreGlobals' have been
introduced as a partial solution, but they need to be made more
robust.
- A more elaborate interactive mode, perhaps with a prompt and
readline support.
- A StructuredText and/or reStructuredText filter would be quite
useful, as would SGML/HTML/XML/XHTML, s-expression, Python,
etc. auto-indenter filters.
- An indexing filter, which can process text and pick out
predefined keywords and thereby setup links to them.
- The ability to rerun diverted material back through the
interpreter. (This can be done, awkwardly, by manually creating
a filter which itself contains an interpreter, but it might be
helpful if this was an all-in-one operation.)
- A caching system that stores off the compilations of repeated
evaluations and executions so that in a persistent environment
the same code does not have to be repeatedly evaluated/executed.
This would probably be a necessity in an Apache module-based
solution. Perhaps caching even to the point of generating pure
PyWM bytecode?
- An option to change the format of the standard EmPy errors in a
traceback.
- Support for some manner of implicitly processed /etc/empyrc
and/or ~/.empyrc file, and of course an option to inhibit its
processing. This can already be accomplished (and with greater
control) via use of EMPY_OPTIONS, though.
- More uniform handling of the preprocessing directives (-I, -D,
-E, -F, and -P), probably mapping directly to methods in the
'Interpreter' class.
- Support for integration with mod_python.
- In simple expressions, a '{...}' suffix has no meaning in Python
(*e.g.*, in Python, '@x(...)' is a call, '@x[...]' is
subscription, but '@x{...}' is illegal). This could be
exploited by having a '{...}' suffix in a simple expression
representing an encapsulation of an expanded string; *e.g.*,
'@bullet{There are @count people here}' would be equivalent to
'@bullet(empy.expand("There are @count people here",
locals()))}'.
- A tool to collect significator information from a hierarchy of
.em files and put them in a database form available for
individual scripts would be extremely useful -- this tool should
be extensible so that users can use it to, say, build ordered
hierarchies of their EmPy files by detecting contextual
information like application-specific links to other EmPy
documents.
- Extensions of the basic EmPy concepts to projects for other
interpreted languages, such as Java, Lua, Ruby, and/or Perl.
- Ignore 'SystemExit' when doing error handling, letting the
exception progagate up? So far no one seems to worry about
this; deliberately exiting early in a template seems to be an
unlikely occurrence. (Furthermore, there are the 'os.abort' and
'os._exit' facilities for terminating without exception
propagation.)
- A new markup which is the equivalent of '$...:...$' in source
control systems, where the left-hand portion represents a
keyword and the right-hand portion represents its value which is
substituted in by the EmPy system.
- The ability to obtain the filename (if relevant) and mode of the
primary output file.
- The ability to redirect multiple streams of output; not
diversions, but rather the ability to write to one file and then
another. Since output would be under the EmPy script's control,
this would imply a useful --no-output option, where by default
no output is written. This would also suggest the usefulness of
all the output file delegates (diversions, filters, abstract
files, etc.) passing unrecognized method calls all the way down
to underlying file object.
- In addition to the em.py script, an additional support library
(non-executable) should be included which includes ancillary
functionality for more advanced features, but which is not
necessary to use EmPy in its basic form as a standalone
executable. Such features would include things like
significator processing, metadata scanning, and advanced
prompting systems.
Release history
- 3.3; 2003 Oct 27. Custom markup '@<...>'; remove separate
pseudomodule instance for greater transparency; deprecate
'interpreter' attribute of pseudomodule; deprecate auxiliary
class name attributes associated with pseudomodule in
preparation for separate support library in 4.0; add
--no-callback-error and --no-bangpath-processing command line
options; add 'atToken' hook.
- 3.2; 2003 Oct 7. Reengineer hooks support to use hook
instances; add -v option; add --relative-path option; reversed
PEP 317 style; modify Unicode support to give less confusing
errors in the case of unknown encodings and error handlers;
relicensed under LGPL.
- 3.1.1; 2003 Sep 20. Add literal '@"..."' markup; add
--pause-at-end command line option; fix improper globals
collision error via the 'sys.stdout' proxy.
- 3.1; 2003 Aug 8. Unicode support (Python 2.0 and above); add
Document and Processor helper classes for processing
significators; add --no-prefix option for suppressing all
markups.
- 3.0.4; 2003 Aug 7. Implement somewhat more robust lvalue
parsing for '@[for]' construct (thanks to Beni Cherniavsky for
inspiration).
- 3.0.3; 2003 Jul 9. Fix bug regarding recursive tuple unpacking
using '@[for]'; add 'empy.saveGlobals', 'empy.restoreGlobals',
and 'empy.defined' functions.
- 3.0.2; 2003 Jun 19. '@?' and '@!' markups for changing the
current context name and line, respectively; add 'update' method
to interpreter; new and renamed context operations,
'empy.setContextName', 'empy.setContextLine',
'empy.pushContext', 'empy.popContext'.
- 3.0.1; 2003 Jun 9. Fix simple bug preventing command line
preprocessing directives (-I, -D, -E, -F, -P) from executing
properly; defensive PEP 317 compliance [defunct].
- 3.0; 2003 Jun 1. Control markups with '@[...]'; remove
substitutions (use control markups instead); support
'@(...?...!...)' for conditional expressions in addition to the
now-deprecated '@(...?...:...)' variety; add acknowledgements
and glossary sections to documentation; rename buffering option
back to -b; add -m option and 'EMPY_PSEUDO' environment variable
for changing the pseudomodule name; add -n option and
'EMPY_NO_OVERRIDE' environment variable for suppressing
'sys.stdout' proxy; rename main error class to 'Error'; add
standalone 'expand' function; add --binary and --chunk-size
options; reengineer parsing system to use Tokens for easy
extensibility; safeguard curly braces in simple expressions
(meaningless in Python and thus likely a typographical error) by
making them a parse error; fix bug involving custom Interpreter
instances ignoring globals argument; distutils support.
- 2.3; 2003 Feb 20. Proper and full support for concurrent and
recursive interpreters; protection from closing the true stdout
file object; detect edge cases of interpreter globals or
'sys.stdout' proxy collisions; add globals manipulation
functions 'empy.getGlobals', 'empy.setGlobals', and
'empy.updateGlobals' which properly preserve the 'empy'
pseudomodule; separate usage info out into easily accessible
lists for easier presentation; have -h option show simple usage
and -H show extened usage; add 'NullFile' utility class.
- 2.2.6; 2003 Jan 30. Fix a bug in the 'Filter.detach' method
(which would not normally be called anyway).
- 2.2.5; 2003 Jan 9. Strip carriage returns out of executed code
blocks for DOS/Windows compatibility.
- 2.2.4; 2002 Dec 23. Abstract Filter interface to use methods
only; add '@[noop: ...]' substitution for completeness and block
commenting [defunct].
- 2.2.3; 2002 Dec 16. Support compatibility with Jython by
working around a minor difference between CPython and Jython in
string splitting.
- 2.2.2; 2002 Dec 14. Include better docstrings for pseudomodule
functions; segue to a dictionary-based options system for
interpreters; add 'empy.clearAllHooks' and 'empy.clearGlobals';
include a short documentation section on embedding interpreters;
fix a bug in significator regular expression.
- 2.2.1; 2002 Nov 30. Tweak test script to avoid writing
unnecessary temporary file; add 'Interpreter.single' method;
expose 'evaluate', 'execute', 'substitute' [defunct], and
'single' methods to the pseudomodule; add (rather obvious)
'EMPY_OPTIONS' environment variable support; add
'empy.enableHooks' and 'empy.disableHooks'; include optimization
to transparently disable hooks until they are actually used.
- 2.2; 2002 Nov 21. Switched to -V option for version
information; 'empy.createDiversion' for creating initially empty
diversion; direct access to diversion objects with
'empy.retrieveDiversion'; environment variable support; removed
--raw long argument (use --raw-errors instead); added quaternary
escape code (well, why not).
- 2.1; 2002 Oct 18. 'empy.atExit' registry separate from hooks to
allow for normal interpreter support; include a benchmark sample
and test.sh verification script; expose 'empy.string' directly;
-D option for explicit defines on command line; remove
ill-conceived support for '@else:' separator in '@[if ...]'
substitution [defunct] ; handle nested substitutions properly
[defunct] ; '@[macro ...]' substitution for creating recallable
expansions [defunct].
- 2.0.1; 2002 Oct 8. Fix missing usage information; fix
after_evaluate hook not getting called; add 'empy.atExit' call
to register values.
- 2.0; 2002 Sep 30. Parsing system completely revamped and
simplified, eliminating a whole class of context-related bugs;
builtin support for buffered filters; support for registering
hooks; support for command line arguments; interactive mode with
-i; significator value extended to be any valid Python
expression.
- 1.5.1; 2002 Sep 24. Allow '@]' to represent unbalanced close
brackets in '@[...]' markups [defunct].
- 1.5; 2002 Sep 18. Escape codes ('@\...'); conditional and
repeated expansion substitutions [defunct] ; replaced with control
markups]; fix a few bugs involving files which do not end in
newlines.
- 1.4; 2002 Sep 7. Fix bug with triple quotes; collapse
conditional and protected expression syntaxes into the single
generalized '@(...)' notation; 'empy.setName' and 'empy.setLine'
functions [deprecated] ; true support for multiple concurrent
interpreters with improved sys.stdout proxy; proper support for
'empy.expand' to return a string evaluated in a subinterpreter
as intended; merged Context and Parser classes together, and
separated out Scanner functionality.
- 1.3; 2002 Aug 24. Pseudomodule as true instance; move toward
more verbose (and clear) pseudomodule functions; fleshed out
diversion model; filters; conditional expressions; protected
expressions; preprocessing with -P (in preparation for
possible support for command line arguments).
- 1.2; 2002 Aug 16. Treat bangpaths as comments; 'empy.quote' for
the opposite process of 'empy.expand'; significators ('@%...'
sequences); -I option; -f option; much improved documentation.
- 1.1.5; 2002 Aug 15. Add a separate 'invoke' function that can be
called multiple times with arguments to simulate multiple runs.
- 1.1.4; 2002 Aug 12. Handle strings thrown as exceptions
properly; use getopt to process command line arguments; cleanup
file buffering with AbstractFile; very slight documentation and
code cleanup.
- 1.1.3; 2002 Aug 9. Support for changing the prefix from within
the 'empy' pseudomodule.
- 1.1.2; 2002 Aug 5. Renamed buffering option [defunct], added -F
option for interpreting Python files from the command line,
fixed improper handling of exceptions from command line options
(-E, -F).
- 1.1.1; 2002 Aug 4. Typo bugfixes; documentation clarification.
- 1.1; 2002 Aug 4. Added option for fully buffering output
(including file opens), executing commands through the command
line; some documentation errors fixed.
- 1.0; 2002 Jul 23. Renamed project to EmPy. Documentation and
sample tweaks; added 'empy.flatten'. Added -a option.
- 0.3; 2002 Apr 14. Extended "simple expression" syntax,
interpreter abstraction, proper context handling, better error
handling, explicit file inclusion, extended samples.
- 0.2; 2002 Apr 13. Bugfixes, support non-expansion of Nones,
allow choice of alternate prefix.
- 0.1.1; 2002 Apr 12. Bugfixes, support for Python 1.5.x, add -r
option.
- 0.1; 2002 Apr 12. Initial early access release.
Author
This module was written by "Erik Max Francis",
http://www.alcyone.com/max/. If you use this software, have
suggestions for future releases, or bug reports, "I'd love to hear
about it", mailto:software@alcyone.com.
Even if you try out EmPy for a project and find it unsuitable, I'd
like to know what stumbling blocks you ran into so they can
potentially be addressed in a future version.
Version
Version 3.3 $Date: 2003/10/27 $ $Author: max $
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cf7e9016cf87e4c8d8b4eeb14917641d
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