<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 21. Using Python</title><meta name="generator" content="DocBook XSL Stylesheets V1.71.1"><link rel="start" href="index.html" title="A-A-P Recipe Executive"><link rel="up" href="user.html" title="Part II. User Manual"><link rel="prev" href="user-issue.html" title="Chapter 20. Issue Tracking"><link rel="next" href="user-porting.html" title="Chapter 22. Porting an Application"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><table width="100%" id="navtable"><tbody><tr><td align="left" class="left" width="33%"><b><a href="http://www.a-a-p.org">A-A-P home page</a></b></td><td align="center" class="center" width="34%"><b><a href="index.html">A-A-P Recipe Executive</a></b></td><td align="right" class="right" width="33%"></td></tr><tr><td align="left" class="left"><a accesskey="p" href="user-issue.html">Prev</a></td><td align="center" class="center">User Manual</td><td align="right" class="right"><a accesskey="n" href="user-porting.html">Next</a></td></tr></tbody></table><hr><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="user-python"></a>Chapter 21. Using Python</h2></div></div></div><p>
Python commands can be used where <span class="application">Aap</span> commands are not sufficient.
This includes flow control, selecting the commands to be executed and
repeating commands.
</p><h2><a name="id2649018"></a>Using Python Lines</h2><p>
Single lines of Python code can be included in the recipe by prepending "@".
This is most often used for flow control:
</p><pre class="programlisting">
@if os.path.isdir("/usr/local/bin"):
:copy $File /usr/local/bin
</pre><p>
You can write multiple Python commands, just prefix a "@" to every line.
Do remember that the amount of indent is used to form command blocks.
The indent that is used excludes the "@" character.
When there is a non-white character after the "@", the "@" is removed.
When there is white space after the "@" it is replaced with a space.
Generally you don't need to worry about this, if the indenting looks right it
probably is.
</p><p>
The main advantage of using single Python lines is that they can be mixed
freely with <span class="application">Aap</span> recipe command lines. You can use Python lines both at
the recipe level and in build commands. Again, just make sure the indent
indicates command blocks.
</p><p>
To learn using Python start at the Python web site:
<a href="http://www.python.org/doc/" target="_top">http://www.python.org/doc/</a>
</p><h2><a name="id2649735"></a>Using Aap variables in Python</h2><p>
You can use all the Aap variables in Python code. You don't use the "$",
Python syntax does not use a dollar for variables.
</p><p>
When using a scope name, as in "_recipe.var", the variable otherwise looks
the same as in Aap commands. But when omitting a scope name it works
differently. While "$var" in Aap searches for "var" in the "_no" scope,
this does not happen for Python. Python only looks in the current scope.
Thus you must explicitly specify "_no.var" in Python code to get the same
effect as "$var" in an Aap command.
</p><p>
In the following example a local variable "system" is used:
</p><pre class="programlisting">
CFLAGS = -DFOO
all:
system = $OSTYPE
@if system == "posix":
@ flags = _recipe.CFLAGS
</pre><p>
The same thing could be done by accessing $OSTYPE directly from Python:
</p><pre class="programlisting">
CFLAGS = -DFOO
all:
@if _no.OSTYPE == "posix":
@ flags = _recipe.CFLAGS
</pre><h2><a name="python-expression"></a>Using Python Expressions</h2><p>
In an assignment, command arguments and most other places a Python expression
can be used in backticks. Expanding this is done before expanding $VAR items,
because this allows the possibility to use the Python expression to result in
the name of a variable. Example:
</p><pre class="programlisting">
foovaridx = 5
Foo = $Src`foovaridx`
</pre><p>
Is equivalent to:
</p><pre class="programlisting">
Foo = $Src5
</pre><p>
The result of the Python expression in backticks should be a string or a list
of strings. A list is automatically converted to a white-separated string of
all list items.
</p><p>
A Python expression cannot be used for the variable name in an assignment.
This doesn't work:
</p><pre class="programlisting">
`varname` = this does not work
</pre><p>
If you really need this, use a Python command instead:
</p><pre class="programlisting">
@eval(varname + ' = "value"')
</pre><p>
When using a function from a module, it must be imported first. Example:
</p><pre class="programlisting">
@from httplib import HTTP
Connection = `HTTP('www.microsoft.com')`
</pre><p>
For your convenience these things are imported for you already:
</p><pre class="programlisting">
from glob import glob
from RecPython import *
</pre><p>
The RecPython module defines the Python functions listed in <a href="ref-python.html" title="Chapter 41. A-A-P Python functions">Chapter 41, <i>A-A-P Python functions</i></a>.
</p><p>
A backtick in the Python expression has to be escaped to avoid it being
recognized as the end of the expression:
</p><pre class="programlisting">
CMD = `my_func("$(`)grep -l foo *.c$(`)")`
</pre><p>
contains the Python expression:
</p><pre class="programlisting">
my_func("`grep -l foo *.c`")
</pre><p>
In the result of the Python expression $ characters are doubled, to avoid them
being interpreted as the start of a variable reference. Otherwise Python
expressions with arbitrary results would always have to be filtered explicitly.
When the resulting string is used the $$ will be reduced to a single $ again.
</p><p>
The result of the expression is used as a string in place of the expression
and the backticks. Example:
</p><pre class="programlisting">
Foo = foo/`glob("*.tmp")`
</pre><p>
Would be equivalent to:
</p><pre class="programlisting">
Foo = foo/one.tmp two.tmp
</pre><p>
Note that "foo/" is only prepended to the whole result, not each
white-separated item. If you do want rc-style expansion, use two commands:
</p><pre class="programlisting">
TT = `glob("*.tmp")`
Foo = foo/$*TT
</pre><p>
Equivalent to:
</p><pre class="programlisting">
Foo = foo/one.tmp foo/two.tmp
</pre><p>
Note that a following attribute is only attached to the last item resulting
from the Python expression.
</p><pre class="programlisting">
Source = `glob('*.c')` {check = md5}
</pre><p>
Can be equivalent to:
</p><pre class="programlisting">
Source = foo.c bar.c {check = md5}
</pre><p>
To apply it to all items, use the <a href="ref-commands.html#cmd-attr">:attr</a>
command:
</p><pre class="programlisting">
Source = `glob('*.c')`
:attr {check = md5} $Source
</pre><p>
Watch out for unexpected results when rc-style expansion is done for $*VAR.
Example:
</p><pre class="programlisting">
VAR = one two
Foo = $*VAR/`glob("*.tmp")`
</pre><p>
Would result in:
</p><pre class="programlisting">
Foo = one/one.tmp two/one.tmp two.tmp
</pre><p>
because the `` part is expanded first, thus the assignment is executed like:
</p><pre class="programlisting">
Foo = $*VAR/one.tmp two.tmp
</pre><p>
The backticks for a Python expression are also recognized inside quotes.
Thus you need to escape the special meaning there:
</p><pre class="programlisting">
Foo = "this$(`)file" that$(`)file
</pre><p>
Backtick expressions can be used inside a string if you really need this:
</p><pre class="programlisting">
DIR = /home/foo /home/bar
:print "`DIR + "/fi le"`"
</pre><p>
results in:
</p><div class="literallayout"><p> "/home/foo /home/bar/fi le"<br>
</p></div><p>
Compare this to:
</p><pre class="programlisting">
:print "$*DIR/fi le"
</pre><p>
which results in:
</p><div class="literallayout"><p> "/home/foo/fi le" "/home/bar/fi le"<br>
</p></div><h2><a name="id2650899"></a>Python Block</h2><p>
A block of Python commands is started with a
<a href="ref-commands.html#cmd-python">:python</a> command. If no
terminator string is specified the python code ends where the indent is equal
to or less than the
<a href="ref-commands.html#cmd-python">:python</a> command:
</p><pre class="programlisting">
Source = foo.c bar.c
:python
for i in items:
Source = Source + " " + i
Target = foo
</pre><p>
Optionally a terminator string may be specified. The indent of the Python
code may then drop below the indent of the
<a href="ref-commands.html#cmd-python">:python</a> command.
</p><p>
The terminator cannot contain white space. A comment may follow. The Python
block continues until the terminator string is found in a line by itself. It
may be preceded and followed by white space and a comment may follow.
Example:
</p><pre class="programlisting">
@if ok:
:print finding include files
:python EOF # start of the Python block
include = glob("include/*.c")
EOF # end of the Python block
</pre><h2><a name="id2650939"></a>Useful Python Items</h2><p>
A list of Python functions defined by <span class="application">Aap</span> can be found in the reference
manual, <a href="ref-python.html" title="Chapter 41. A-A-P Python functions">Chapter 41, <i>A-A-P Python functions</i></a>.
</p><pre class="programlisting">
VAR = `os.environ.get('VAR', 'default')`
</pre><p>
Obtain environment variable $VAR. If it is not set use "default".
</p><pre class="programlisting">
@os.environ["PATH"] = mypath
</pre><p>
Set an environment variable.
</p><pre class="programlisting">
files = `glob("*.ext")`
</pre><p>
Obtain a list of files matching "*.ext". Aap will take care of turning the
list that glob() returns into a string, using quotes where needed.
</p><p>
The difference with using "*.ext" directly is that the expansion is done right
here, not later when $files is used. The catch with using glob() here is that
when a file name contains a wildcard character it may be expanded again. So
long as that expansion fails or matches the same file name it is still OK, but
it becomes rather unpredictable. Use <a href="ref-python.html#python-wildescape">wildescape()</a> when needed.
</p><pre class="programlisting">
choice = `raw_input("Enter the value: ")`
</pre><p>
Prompt the user to enter a value.
</p><pre class="programlisting">
tempfile = `tempfname()`
</pre><p>
Get a file name to use for temporary files. The file will not exist.
See <a href="ref-python.html#python-tempfname">tempfname()</a>.
</p><p>
If you create it you need to make sure it is deleted afterwards.
Example:
</p><pre class="programlisting">
tempfile = `tempfname()`
@try:
:print >$tempfile start of file
:print >>$tempfile $this variable may not exist and cause an error
:cat $tempfile
@finally:
# this is executed whether there is an error or not
:del $tempfile
</pre><p>
Exception handling can be useful to handle situations where you know something
might fail. Example:
</p><pre class="programlisting">
@try:
:sys links -dump exec.html >exec.txt
@except:
:sys lynx -dump -nolist exec.html >exec.txt
</pre><p>
This will execute the "links" command. If this fails for some reason (e.g.,
because a new version of "links" does not support the "-dump" argument) then
the "lynx" command will be used.
</p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="user-issue.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="user.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="user-porting.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 20. Issue Tracking </td><td width="20%" align="center"><a accesskey="h" href="index.html">
Contents</a></td><td width="40%" align="right" valign="top"> Chapter 22. Porting an Application</td></tr></table></div></body></html>
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contrib-release
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a6d417e36f6bb1154f4c003e6717e298
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files
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