<html>
<head>
<title>Appendix C: Zope Page Templates Reference</title>
</head>
<body bgcolor="#FFFFFF">
<h1>Appendix C: Zope Page Templates Reference</h1>
<p> Zope Page Templates are an HTML/XML generation tool. This appendix
is a reference to Zope Page Templates standards: Tag Attribute
Language (TAL), TAL Expression Syntax (TALES), and Macro Expansion
TAL (METAL).</p><h2> TAL Overview</h2>
<p> The <em>Template Attribute Language</em> (TAL) standard is an attribute
language used to create dynamic templates. It allows elements of a
document to be replaced, repeated, or omitted.</p><p> The statements of TAL are XML attributes from the TAL namespace.
These attributes can be applied to an XML or HTML document in order
to make it act as a template.</p><p> A <strong>TAL statement</strong> has a name (the attribute name) and a body (the
attribute value). For example, an <code>content</code> statement might look
like <code>tal:content="string:Hello"</code>. The element on which a statement
is defined is its <strong>statement element</strong>. Most TAL statements
require expressions, but the syntax and semantics of these
expressions are not part of TAL. TALES is recommended for this
purpose.</p><h3> TAL Namespace</h3>
<p> The TAL namespace URI and recommended alias are currently defined
as:<pre> xmlns:tal="http://xml.zope.org/namespaces/tal"</pre>
</p><p> This is not a URL, but merely a unique identifier. Do not expect
a browser to resolve it successfully.</p><p> Zope does not require an XML namespace declaration when creating
templates with a content-type of <code>text/html</code>. However, it does
require an XML namespace declaration for all other content-types.</p><h3> TAL Statements </h3>
<p> These are the tal statements:</p><ul>
<li>tal:attributes - dynamically change
element attributes.</li>
<li>tal:define - define variables.</li>
<li>tal:condition - test conditions.</li>
<li>tal:content - replace the content of an
element.</li>
<li>tal:omit-tag - remove an element, leaving
the content of the element.</li>
<li>tal:on-error - handle errors.</li>
<li>tal:repeat - repeat an element.</li>
<li>tal:replace - replace the content of an
element and remove the element leaving the content.</li>
</ul>
<p> Expressions used in statements may return values of any type,
although most statements will only accept strings, or will convert
values into a string representation. The expression language must
define a value named <em>nothing</em> that is not a string. In
particular, this value is useful for deleting elements or
attributes.</p><h3> Order of Operations</h3>
<p> When there is only one TAL statement per element, the order in
which they are executed is simple. Starting with the root
element, each element's statements are executed, then each of its
child elements is visited, in order, to do the same.</p><p> Any combination of statements may appear on the same elements,
except that the <code>content</code> and <code>replace</code> statements may not appear
together.</p><p> When an element has multiple statements, they are executed in this
order:</p><ol>
<li> <code>define</code></li>
<li> <code>condition</code></li>
<li> <code>repeat</code></li>
<li> <code>content</code> or <code>replace</code></li>
<li> <code>attributes</code></li>
<li> <code>omit-tag</code></li>
</ol>
<p> Since the <code>on-error</code> statement is only invoked when an error occurs,
it does not appear in the list. </p><p> The reasoning behind this ordering goes like this: You often want
to set up variables for use in other statements, so <code>define</code> comes
first. The very next thing to do is decide whether this element
will be included at all, so <code>condition</code> is next; since the
condition may depend on variables you just set, it comes after
<code>define</code>. It is valuable be able to replace various parts of an
element with different values on each iteration of a repeat, so
<code>repeat</code> is next. It makes no sense to replace attributes and
then throw them away, so <code>attributes</code> is last. The remaining
statements clash, because they each replace or edit the statement
element.</p><h3> See Also</h3>
<p> TALES Overview</p><p> METAL Overview</p><p> tal:attributes</p><p> tal:define</p><p> tal:condition</p><p> tal:content</p><p> tal:omit-tag</p><p> tal:on-error</p><p> tal:repeat</p><p> tal:replace</p><h2> attributes: Replace element attributes</h2>
<h3> Syntax</h3>
<p> <code>tal:attributes</code> syntax:<pre> argument ::= attribute_statement [';' attribute_statement]*
attribute_statement ::= attribute_name expression
attribute_name ::= [namespace ':'] Name
namespace ::= Name</pre>
</p><p> <em>Note: If you want to include a semi-colon (;) in an <code>expression</code>,
it must be escaped by doubling it (;;).</em></p><h3> Description</h3>
<p> The <code>tal:attributes</code> statement replaces the value of an attribute
(or creates an attribute) with a dynamic value. You can qualify an
attribute name with a namespace prefix, for example <code>html:table</code>, if
you are generating an XML document with multiple namespaces. The
value of each expression is converted to a string, if necessary.</p><p> If the expression associated with an attribute assignment evaluates
to <em>nothing</em>, then that attribute is deleted from the statement
element. If the expression evaluates to <em>default</em>, then that
attribute is left unchanged. Each attribute assignment is
independent, so attributes may be assigned in the same statement in
which some attributes are deleted and others are left alone.</p><p> If you use <code>tal:attributes</code> on an element with an active
<code>tal:replace</code> command, the <code>tal:attributes</code> statement is ignored.</p><p> If you use <code>tal:attributes</code> on an element with a <code>tal:repeat</code>
statement, the replacement is made on each repetition of the
element, and the replacement expression is evaluated fresh for each
repetition.</p><h3> Examples</h3>
<p> Replacing a link:<pre> <a href="/sample/link.html"
tal:attributes="href here/sub/absolute_url"></pre>
</p><p> Replacing two attributes:<pre> <textarea rows="80" cols="20"
tal:attributes="rows request/rows;cols request/cols"></pre>
</p><h2> condition: Conditionally insert or remove an element</h2>
<h3> Syntax</h3>
<p> <code>tal:condition</code> syntax:<pre> argument ::= expression</pre>
</p><h3> Description</h3>
<p> The <code>tal:condition</code> statement includes the statement element in the
template only if the condition is met, and omits it otherwise. If
its expression evaluates to a <em>true</em> value, then normal processing
of the element continues, otherwise the statement element is
immediately removed from the template. For these purposes, the
value <em>nothing</em> is false, and <em>default</em> has the same effect as
returning a true value.</p><p> <em>Note: Zope considers missing variables, None, zero, empty strings,
and empty sequences false; all other values are true.</em></p><h3> Examples</h3>
<p> Test a variable before inserting it (the first example tests for
existence and truth, while the second only tests for existence):<pre> <p tal:condition="request/message | nothing"
tal:content="request/message">message goes here</p>
<p tal:condition="exists:request/message"
tal:content="request/message">message goes here</p></pre>
</p><p> Test for alternate conditions:<pre> <div tal:repeat="item python:range(10)">
<p tal:condition="repeat/item/even">Even</p>
<p tal:condition="repeat/item/odd">Odd</p>
</div></pre>
</p><h2> content: Replace the content of an element</h2>
<h3> Syntax</h3>
<p> <code>tal:content</code> syntax:<pre> argument ::= (['text'] | 'structure') expression</pre>
</p><h3> Description</h3>
<p> Rather than replacing an entire element, you can insert text or
structure in place of its children with the <code>tal:content</code>
statement. The statement argument is exactly like that of
<code>tal:replace</code>, and is interpreted in the same fashion. If the
expression evaluates to <em>nothing</em>, the statement element is left
childless. If the expression evaluates to <em>default</em>, then the
element's contents are unchanged.</p><p> <em>Note: The default replacement behavior is <code>text</code>.</em></p><h3> Examples</h3>
<p> Inserting the user name:<pre> <p tal:content="user/getUserName">Fred Farkas</p></pre>
</p><p> Inserting HTML/XML:<pre> <p tal:content="structure here/getStory">marked <b>up</b>
content goes here.</p></pre>
</p><h3> See Also</h3>
<p> <code>tal:replace</code></p><h2> define: Define variables</h2>
<h3> Syntax</h3>
<p> <code>tal:define</code> syntax:<pre> argument ::= define_scope [';' define_scope]*
define_scope ::= (['local'] | 'global') define_var
define_var ::= variable_name expression
variable_name ::= Name</pre>
</p><p> <em>Note: If you want to include a semi-colon (;) in an <code>expression</code>,
it must be escaped by doubling it (;;).</em></p><h3> Description</h3>
<p> The <code>tal:define</code> statement defines variables. You can define two
different kinds of TAL variables: local and global. When you
define a local variable in a statement element, you can only use
that variable in that element and the elements it contains. If
you redefine a local variable in a contained element, the new
definition hides the outer element's definition within the inner
element. When you define a global variables, you can use it in
any element processed after the defining element. If you redefine
a global variable, you replace its definition for the rest of the
template.</p><p> <em>Note: local variables are the default</em></p><p> If the expression associated with a variable evaluates to
<em>nothing</em>, then that variable has the value <em>nothing</em>, and may be
used as such in further expressions. Likewise, if the expression
evaluates to <em>default</em>, then the variable has the value <em>default</em>,
and may be used as such in further expressions.</p><h3> Examples</h3>
<p> Defining a global variable:<pre> tal:define="global company_name string:Zope Corp, Inc."</pre>
</p><p> Defining two variables, where the second depends on the first:<pre> tal:define="mytitle template/title; tlen python:len(mytitle)"</pre>
</p><h2> omit-tag: Remove an element, leaving its contents</h2>
<h3> Syntax</h3>
<p> <code>tal:omit-tag</code> syntax:<pre> argument ::= [ expression ]</pre>
</p><h3> Description</h3>
<p> The <code>tal:omit-tag</code> statement leaves the contents of a tag in place
while omitting the surrounding start and end tag.</p><p> If its expression evaluates to a <em>false</em> value, then normal
processing of the element continues and the tag is not omitted.
If the expression evaluates to a <em>true</em> value, or there is no
expression, the statement tag is replaced with its contents. </p><p> Zope treats empty strings, empty sequences, zero, None, <em>nothing</em>,
and <em>default</em> at false. All other values are considered true.</p><h3> Examples</h3>
<p> Unconditionally omitting a tag:<pre> <div tal:omit-tag="" comment="This tag will be removed">
<i>...but this text will remain.</i>
</div></pre>
</p><p> Conditionally omitting a tag:<pre> <b tal:omit-tag="not:bold">I may be bold.</b></pre>
</p><p> The above example will omit the <code>b</code> tag if the variable <code>bold</code> is
false.</p><p> Creating ten paragraph tags, with no enclosing tag:<pre> <span tal:repeat="n python:range(10)"
tal:omit-tag="">
<p tal:content="n">1</p>
</span></pre>
</p><h2> on-error: Handle errors</h2>
<h3> Syntax</h3>
<p> <code>tal:on-error</code> syntax:<pre> argument ::= (['text'] | 'structure') expression</pre>
</p><h3> Description</h3>
<p> The <code>tal:on-error</code> statement provides error handling for your
template. When a TAL statement produces an error, the TAL
interpreter searches for a <code>tal:on-error</code> statement on the same
element, then on the enclosing element, and so forth. The first
<code>tal:on-error</code> found is invoked. It is treated as a <code>tal:content</code>
statement.</p><p> A local variable <code>error</code> is set. This variable has these
attributes:<dl>
<dt> <code>type</code></dt>
<dd>the exception type</dd>
<dt> <code>value</code></dt>
<dd>the exception instance</dd>
<dt> <code>traceback</code></dt>
<dd>the traceback object</dd>
</dl>
</p><p> The simplest sort of <code>tal:on-error</code> statement has a literal error
string or <em>nothing</em> for an expression. A more complex handler may
call a script that examines the error and either emits error text
or raises an exception to propagate the error outwards. </p><h3> Examples</h3>
<p> Simple error message:<pre> <b tal:on-error="string: Username is not defined!"
tal:content="here/getUsername">Ishmael</b></pre>
</p><p> Removing elements with errors:<pre> <b tal:on-error="nothing"
tal:content="here/getUsername">Ishmael</b></pre>
</p><p> Calling an error-handling script:<pre> <div tal:on-error="structure here/errorScript">
...
</div></pre>
</p><p> Here's what the error-handling script might look like:<pre> ## Script (Python) "errHandler"
##bind namespace=_
##
error=_['error']
if error.type==ZeroDivisionError:
return "<p>Can't divide by zero.</p>"
else
return """<p>An error ocurred.</p>
<p>Error type: %s</p>
<p>Error value: %s</p>""" % (error.type,
error.value)</pre>
</p><h3> See Also</h3>
<p> <a href="http://www.python.org/doc/current/tut/node10.html">Python Tutorial: Errors and
Exceptions</a></p><p> <a href="http://www.python.org/doc/current/lib/module-exceptions.html">Python Built-in
Exceptions</a></p><h2> repeat: Repeat an element</h2>
<h3> Syntax</h3>
<p> <code>tal:repeat</code> syntax:<pre> argument ::= variable_name expression
variable_name ::= Name</pre>
</p><h3> Description</h3>
<p> The <code>tal:repeat</code> statement replicates a sub-tree of your document
once for each item in a sequence. The expression should evaluate
to a sequence. If the sequence is empty, then the statement
element is deleted, otherwise it is repeated for each value in the
sequence. If the expression is <em>default</em>, then the element is
left unchanged, and no new variables are defined.</p><p> The <code>variable_name</code> is used to define a local variable and a
repeat variable. For each repetition, the local variable is set to
the current sequence element, and the repeat variable is set to an
iteration object.</p><h3> Repeat Variables</h3>
<p> You use repeat variables to access information about the current
repetition (such as the repeat index). The repeat variable has
the same name as the local variable, but is only accessible
through the built-in variable named <code>repeat</code>.</p><h4> The following information is available from the repeat variable:</h4>
<ul>
<li><em>index</em> - repetition number, starting from zero.</li>
<li><em>number</em> - repetition number, starting from one.</li>
<li><em>even</em> - true for even-indexed repetitions (0, 2, 4, ...).</li>
<li><em>odd</em> - true for odd-indexed repetitions (1, 3, 5, ...).</li>
<li><em>start</em> - true for the starting repetition (index 0).</li>
<li><em>end</em> - true for the ending, or final, repetition.</li>
<li><em>first</em> - true for the first item in a group - see note below</li>
<li><em>last</em> - true for the last item in a group - see note below</li>
<li><em>length</em> - length of the sequence, which will be the total number
of repetitions.</li>
<li><em>letter</em> - repetition number as a lower-case letter: "a" -
"z", "aa" - "az", "ba" - "bz", ..., "za" - "zz", "aaa" - "aaz",
and so forth.</li>
<li><em>Letter</em> - upper-case version of <em>letter</em>.</li>
<li><em>roman</em> - repetition number as a lower-case roman numeral:
"i", "ii", "iii", "iv", "v", etc.</li>
<li><em>Roman</em> - upper-case version of <em>roman</em>.</li>
</ul>
<p> You can access the contents of the repeat variable using path
expressions or Python expressions. In path expressions, you write
a three-part path consisting of the name <code>repeat</code>, the statement
variable's name, and the name of the information you want, for
example, <code>repeat/item/start</code>. In Python expressions, you use
normal dictionary notation to get the repeat variable, then
attribute access to get the information, for example,
"python:repeat['item'].start".</p><p> Note that <code>first</code> and <code>last</code> are intended for use with sorted
sequences. They try to divide the sequence into group of items
with the same value. If you provide a path, then the value
obtained by following that path from a sequence item is used for
grouping, otherwise the value of the item is used. You can
provide the path by passing it as a parameter, as in
"python:repeat['item'].first('color')", or by appending it to the
path from the repeat variable, as in "repeat/item/first/color".</p><h3> Examples</h3>
<h4> Iterating over a sequence of strings:: </h4>
<p> <p tal:repeat="txt python:'one', <code>two</code>, 'three'">
<span tal:replace="txt" />
</p></p><p> Inserting a sequence of table rows, and using the repeat variable
to number the rows:<pre> <table>
<tr tal:repeat="item here/cart">
<td tal:content="repeat/item/number">1</td>
<td tal:content="item/description">Widget</td>
<td tal:content="item/price">$1.50</td>
</tr>
</table></pre>
</p><p> Nested repeats:<pre> <table border="1">
<tr tal:repeat="row python:range(10)">
<td tal:repeat="column python:range(10)">
<span tal:define="x repeat/row/number;
y repeat/column/number;
z python:x*y"
tal:replace="string:$x * $y = $z">1 * 1 = 1</span>
</td>
</tr>
</table></pre>
</p><p> Insert objects. Seperates groups of objects by meta-type by
drawing a rule between them:<pre> <div tal:repeat="object objects">
<h2 tal:condition="repeat/object/first/meta_type"
tal:content="object/meta_type">Meta Type</h2>
<p tal:content="object/getId">Object ID</p>
<hr tal:condition="repeat/object/last/meta_type" />
</div></pre>
</p><p> Note, the objects in the above example should already be sorted by
meta-type.</p><h2> replace: Replace an element</h2>
<h3> Syntax</h3>
<p> <code>tal:replace</code> syntax:<pre> argument ::= (['text'] | 'structure') expression</pre>
</p><h3> Description </h3>
<p> The <code>tal:replace</code> statement replaces an element with dynamic
content. It replaces the statement element with either text or a
structure (unescaped markup). The body of the statement is an
expression with an optional type prefix. The value of the
expression is converted into an escaped string if you prefix the
expression with <code>text</code> or omit the prefix, and is inserted
unchanged if you prefix it with <code>structure</code>. Escaping consists of
converting "&" to "&amp;", "<" to "&lt;", and
">" to "&gt;".</p><p> If the value is <em>nothing</em>, then the element is simply removed. If
the value is <em>default</em>, then the element is left unchanged.</p><h3> Examples</h3>
<p> The two ways to insert the title of a template:<pre> <span tal:replace="template/title">Title</span>
<span tal:replace="text template/title">Title</span></pre>
</p><p> Inserting HTML/XML:<pre> <div tal:replace="structure table" /></pre>
</p><p> Inserting nothing:<pre> <div tal:replace="nothing">This element is a comment.</div></pre>
</p><h3> See Also</h3>
<p> <code>tal:content</code></p><h2> TALES Overview</h2>
<p> The <em>Template Attribute Language Expression Syntax</em> (TALES) standard
describes expressions that supply TAL and
METAL with data. TALES is <em>one</em> possible expression
syntax for these languages, but they are not bound to this
definition. Similarly, TALES could be used in a context having
nothing to do with TAL or METAL.</p><p> TALES expressions are described below with any delimiter or quote
markup from higher language layers removed. Here is the basic
definition of TALES syntax:<pre> Expression ::= [type_prefix ':'] String
type_prefix ::= Name</pre>
</p><p> Here are some simple examples:<pre> a/b/c
path:a/b/c
nothing
path:nothing
python: 1 + 2
string:Hello, ${user/getUserName}</pre>
</p><p> The optional <em>type prefix</em> determines the semantics and syntax of
the <em>expression string</em> that follows it. A given implementation of
TALES can define any number of expression types, with whatever
syntax you like. It also determines which expression type is
indicated by omitting the prefix.</p><p> If you do not specify a prefix, Zope assumes that the expression is
a <em>path</em> expression.</p><h3> TALES Expression Types</h3>
<p> These are the TALES expression types supported by Zope:</p><ul>
<li>path expressions - locate a value by its path.</li>
<li>exists expressions - test whether a path is valid.</li>
<li>nocall expressions - locate an object by its path.</li>
<li>not expressions - negate an expression</li>
<li>string expressions - format a string</li>
<li>python expressions - execute a Python
expression</li>
</ul>
<h3> Built-in Names</h3>
<p> These are the names that always available to TALES expressions in Zope:</p><ul>
<li><em>nothing</em> - special value used by to represent
a <em>non-value</em> (e.g. void, None, Nil, NULL).</li>
<li><em>default</em> - special value used to specify that
existing text should not be replaced. See the documentation for
individual TAL statements for details on how they interpret
<em>default</em>.</li>
<li><em>options</em> - the <em>keyword</em> arguments passed to the template. These
are generally available when a template is called from Methods
and Scripts, rather than from the web.</li>
<li><em>repeat</em> - the <code>repeat</code> variables; see the
tal:repeat documentation.</li>
<li><em>attrs</em> - a dictionary containing the initial values of the
attributes of the current statement tag.</li>
<li><em>CONTEXTS</em> - the list of standard names (this list). This can be
used to access a built-in variable that has been hidden by a local
or global variable with the same name.</li>
<li><em>root</em> - the system's top-most object: the Zope root folder.</li>
<li><em>here</em> - the object to which the template is being applied.</li>
<li><em>container</em> - The folder in which the template is located.</li>
<li><em>template</em> - the template itself.</li>
<li><em>request</em> - the publishing request object.</li>
<li><em>user</em> - the authenticated user object.</li>
<li><em>modules</em> - a collection through which Python modules and
packages can be accessed. Only modules which are approved by
the Zope security policy can be accessed.</li>
</ul>
<p> Note the names <code>root</code>, <code>here</code>, <code>container</code>, <code>template</code>, <code>request</code>,
<code>user</code>, and <code>modules</code> are optional names supported by Zope, but
are not required by the TALES standard.</p><h3> See Also</h3>
<p> TAL Overview</p><p> METAL Overview</p><p> exists expressions</p><p> nocall expressions</p><p> not expressions</p><p> string expressions</p><p> path expressions</p><p> python expressions</p><h2> TALES Exists expressions</h2>
<h3> Syntax</h3>
<p> Exists expression syntax:<pre> exists_expressions ::= 'exists:' path_expression</pre>
</p><h3> Description</h3>
<p> Exists expressions test for the existence of paths. An exists
expression returns true when the path expressions following it
expression returns a value. It is false when the path expression
cannot locate an object.</p><h3> Examples</h3>
<p> Testing for the existence of a form variable:<pre> <p tal:condition="not:exists:request/form/number">
Please enter a number between 0 and 5
</p></pre>
</p><p> Note that in this case you can't use the expression,
<code>not:request/form/number</code>, since that expression will be true if
the <code>number</code> variable exists and is zero.</p><h2> TALES Nocall expressions</h2>
<h3> Syntax</h3>
<p> Nocall expression syntax:<pre> nocall_expression ::= 'nocall:' path_expression</pre>
</p><h3> Description</h3>
<p> Nocall expressions avoid rendering the results of a path
expression.</p><p> An ordinary path expression tries to render the object that it
fetches. This means that if the object is a function, Script,
Method, or some other kind of executable thing, then expression
will evaluate to the result of calling the object. This is
usually what you want, but not always. For example, if you want
to put a DTML Document into a variable so that you can refer to
its properties, you can't use a normal path expression because it
will render the Document into a string.</p><h3> Examples</h3>
<p> Using nocall to get the properties of a document:<pre> <span tal:define="doc nocall:here/aDoc"
tal:content="string:${doc/getId}: ${doc/title}">
Id: Title</span></pre>
</p><p> Using nocall expressions on a functions:<pre> <p tal:define="join nocall:modules/string/join"></pre>
</p><p> This example defines a variable <code>join</code> which is bound to the
<code>string.join</code> function.</p><h2> TALES Not expressions</h2>
<h3> Syntax</h3>
<p> Not expression syntax:<pre> not_expression ::= 'not:' expression</pre>
</p><h3> Description</h3>
<p> Not expression evaluate the expression string (recursively) as a
full expression, and returns the boolean negation of its value. If
the expression supplied does not evaluate to a boolean value,
<em>not</em> will issue a warning and <em>coerce</em> the expression's value
into a boolean type based on the following rules:</p><ol>
<li> the number 0 is <em>false</em></li>
<li> numbers > 0 are <em>true</em></li>
<li> an empty string or other sequence is <em>false</em></li>
<li> a non-empty string or other sequence is <em>true</em></li>
<li> a <em>non-value</em> (e.g. void, None, Nil, NULL, etc) is <em>false</em></li>
<li> all other values are implementation-dependent.</li>
</ol>
<p> If no expression string is supplied, an error should be generated.</p><p> Zope considers all objects not specifically listed above as
<em>false</em> (including negative numbers) to be <em>true</em>.</p><h3> Examples</h3>
<p> Testing a sequence:<pre> <p tal:condition="not:here/objectIds">
There are no contained objects.
</p></pre>
</p><h2> TALES Path expressions</h2>
<h3> Syntax</h3>
<p> Path expression syntax:<pre> PathExpr ::= Path [ '|' Path ]*
Path ::= variable [ '/' URL_Segment ]*
variable ::= Name</pre>
</p><h3> Description</h3>
<p> A path expression consists of one or more <em>paths</em> separated by
vertical bars (|). A path consists of one or more non-empty
strings separated by slashes. The first string must be a variable
name (built-in variable or a user defined variable), and the
remaining strings, the <em>path segments</em>, may contain letters,
digits, spaces, and the punctuation characters underscore, dash,
period, comma, and tilde.</p><p> For example:<pre> request/cookies/oatmeal
nothing
here/some-file 2001_02.html.tar.gz/foo
root/to/branch | default
request/name | string:Anonymous Coward</pre>
</p><p> When a path expression is evaluated, Zope attempts to traverse the
path, from left to right, until it succeeds or runs out of paths
segments. To traverse a path, it first fetches the object stored
in the variable. For each path segment, it traverses from the
current object to the subobject named by the path
segment. Subobjects are located according to standard Zope
traversal rules (via getattr, getitem, or traversal hooks).</p><p> Once a path has been successfully traversed, the resulting object
is the value of the expression. If it is a callable object, such
as a method or template, it is called.</p><p> If a traversal step fails, evaluation immediately proceeds to the next
path. If there are no further paths, an error results.</p><p> The expression in a series of paths seperated by vertical bars can
be any TALES expression. For example, 'request/name |
string:Anonymous Coward'. This is useful chiefly for providing
default values such as strings and numbers which are not
expressable as path expressions.</p><p> If no path is given the result is <em>nothing</em>.</p><p> Since every path must start with a variable name, you need a set
of starting variables that you can use to find other objects and
values. See the TALES overview for a list of
built-in variables. Since variable names are looked up first in
locals, then in globals, then in this list, these names act just
like built-ins in Python; They are always available, but they can
be shadowed by a global or local variable declaration. You can
always access the built-in names explicitly by prefixing them with
<em>CONTEXTS</em>. (e.g. CONTEXTS/root, CONTEXTS/nothing, etc).</p><h3> Examples</h3>
<p> Inserting a cookie variable or a property:<pre> <span tal:replace="request/cookies/pref | here/pref">
preference
</span></pre>
</p><p> Inserting the user name:<pre> <p tal:content="user/getUserName">
User name
</p></pre>
</p><h2> TALES Python expressions</h2>
<h3> Syntax</h3>
<p> Python expression syntax:<pre> Any valid Python language expression</pre>
</p><h3> Description</h3>
<p> Python expressions evaluate Python code in a security-restricted
environment. Python expressions offer the same facilities as those
available in Python-based Scripts and DTML variable expressions.</p><h4> Security Restrictions</h4>
<p> Python expressions are subject to the same security restrictions
as Python-based scripts. These restrictions include:</p><dl>
<dt> access limits</dt>
<dd>Python expressions are subject to Zope
permission and role security restrictions. In addition,
expressions cannot access objects whose names begin with
underscore.</dd>
<dt> write limits</dt>
<dd>Python expressions cannot change attributes of
Zope objects.</dd>
</dl>
<p> Despite these limits malicious Python expressions can cause
problems. See The Zope Book for more information.</p><h4> Built-in Functions</h4>
<p> Python expressions have the same built-ins as Python-based
Scripts with a few additions.</p><p> These standard Python built-ins are available: <code>None</code>, <code>abs</code>,
<code>apply</code>, <code>callable</code>, <code>chr</code>, <code>cmp</code>, <code>complex</code>, <code>delattr</code>,
<code>divmod</code>, <code>filter</code>, <code>float</code>, <code>getattr</code>, <code>hash</code>, <code>hex</code>, <code>int</code>,
<code>isinstance</code>, <code>issubclass</code>, <code>list</code>, <code>len</code>, <code>long</code>, <code>map</code>, <code>max</code>,
<code>min</code>, <code>oct</code>, <code>ord</code>, <code>repr</code>, <code>round</code>, <code>setattr</code>, <code>str</code>, <code>tuple</code>.</p><p> The <code>range</code> and <code>pow</code> functions are available and work the same
way they do in standard Python; however, they are limited to
keep them from generating very large numbers and sequences. This
limitation helps protect against denial of service attacks.</p><p> In addition, these utility functions are available: <code>DateTime</code>,
<code>test</code>, and <code>same_type</code>. See DTML
functions for more
information on these functions.</p><p> Finally, these functions are available in Python expressions,
but not in Python-based scripts:</p><dl>
<dt> <code>path(string)</code></dt>
<dd>Evaluate a TALES path
expression.</dd>
<dt> <code>string(string)</code></dt>
<dd>Evaluate a TALES string
expression.</dd>
<dt> <code>exists(string)</code></dt>
<dd>Evaluates a TALES exists
expression.</dd>
<dt> <code>nocall(string)</code></dt>
<dd>Evaluates a TALES nocall
expression.</dd>
</dl>
<h4> Python Modules</h4>
<p> A number of Python modules are available by default. You can
make more modules available. You can access modules either via
path expressions (for example 'modules/string/join') or in
Python with the <code>modules</code> mapping object (for example
'modules["string"].join'). Here are the default modules:</p><dl>
<dt> <code>string</code></dt>
<dd>The standard <a href="http://www.python.org/doc/current/lib/module-string.html">Python string
module</a>. Note:
most of the functions in the module are also available as
methods on string objects.</dd>
<dt> <code>random</code></dt>
<dd>The standard <a href="http://www.python.org/doc/current/lib/module-random.html">Python random
module</a>.</dd>
<dt> <code>math</code></dt>
<dd>The standard <a href="http://www.python.org/doc/current/lib/module-math.html">Python math
module</a>.</dd>
<dt> <code>sequence</code></dt>
<dd>A module with a powerful sorting function. See
sequence for more information.</dd>
<dt> <code>Products.PythonScripts.standard</code></dt>
<dd>Various HTML formatting
functions available in DTML. See
Products.PythonScripts.standard
for more information.</dd>
<dt> <code>ZTUtils</code></dt>
<dd>Batch processing facilities similar to those
offered by <code>dtml-in</code>. See ZTUtils
for more information.</dd>
<dt> <code>AccessControl</code></dt>
<dd>Security and access checking facilities. See
AccessControl for more
information.</dd>
</dl>
<h3> Examples</h3>
<p> Using a module usage (pick a random choice from a list):<pre> <span tal:replace="python:modules['random'].choice(['one',
'two', 'three', 'four', 'five'])">
a random number between one and five
</span></pre>
</p><p> String processing (capitalize the user name):<pre> <p tal:content="python:user.getUserName().capitalize()">
User Name
</p></pre>
</p><p> Basic math (convert an image size to megabytes):<pre> <p tal:content="python:image.getSize() / 1048576.0">
12.2323
</p></pre>
</p><p> String formatting (format a float to two decimal places):<pre> <p tal:content="python:'%0.2f' % size">
13.56
</p></pre>
</p><h2> TALES String expressions</h2>
<h3> Syntax</h3>
<p> String expression syntax:<pre> string_expression ::= ( plain_string | [ varsub ] )*
varsub ::= ( '$' Path ) | ( '${' Path '}' )
plain_string ::= ( '$$' | non_dollar )*
non_dollar ::= any character except '$'</pre>
</p><h3> Description</h3>
<p> String expressions interpret the expression string as text. If no
expression string is supplied the resulting string is <em>empty</em>. The
string can contain variable substitutions of the form <code>$name</code> or
<code>${path}</code>, where <code>name</code> is a variable name, and <code>path</code> is a
path expression.
The escaped string value of the path expression is inserted into
the string. To prevent a <code>$</code> from being interpreted this way, it
must be escaped as <code>$$</code>.</p><h3> Examples</h3>
<p> Basic string formatting:<pre> <span tal:replace="string:$this and $that">
Spam and Eggs
</span></pre>
</p><p> Using paths:<pre> <p tal:content="total: ${request/form/total}">
total: 12
</p></pre>
</p><p> Including a dollar sign:<pre> <p tal:content="cost: $$$cost">
cost: $42.00
</p></pre>
</p><h2> METAL Overview</h2>
<p> The <em>Macro Expansion Template Attribute Language</em> (METAL) standard
is a facility for HTML/XML macro preprocessing. It can be used in
conjunction with or independently of TAL and
TALES.</p><p> Macros provide a way to define a chunk of presentation in one
template, and share it in others, so that changes to the macro are
immediately reflected in all of the places that share it.
Additionally, macros are always fully expanded, even in a template's
source text, so that the template appears very similar to its final
rendering.</p><h3> METAL Namespace</h3>
<p> The METAL namespace URI and recommended alias are currently
defined as:<pre> xmlns:metal="http://xml.zope.org/namespaces/metal"</pre>
</p><p> Just like the TAL namespace URI, this URI is not attached to a web
page; it's just a unique identifier.</p><p> Zope does not require an XML namespace declaration when creating
templates with a content-type of <code>text/html</code>. However, it does
require an XML namespace declaration for all other content-types.</p><h3> METAL Statements </h3>
<p> METAL defines a number of statements:</p><ul>
<li>metal:define-macro - Define a macro.</li>
<li>metal:use-macro - Use a macro.</li>
<li>metal:define-slot - Define a macro
customization point.</li>
<li>metal:fill-slot - Customize a macro.</li>
</ul>
<p> Although METAL does not define the syntax of expression
non-terminals, leaving that up to the implementation, a canonical
expression syntax for use in METAL arguments is described in
TALES Specification.</p><h3> See Also</h3>
<p> TAL Overview</p><p> TALES Overview</p><p> metal:define-macro</p><p> metal:use-macro</p><p> metal:define-slot</p><p> metal:fill-slot</p><h2> define-macro: Define a macro</h2>
<h3> Syntax</h3>
<p> <code>metal:define-macro</code> syntax:<pre> argument ::= Name</pre>
</p><h3> Description</h3>
<p> The <code>metal:define-macro</code> statement defines a macro. The macro is
named by the statement expression, and is defined as the element
and its sub-tree.</p><p> In Zope, a macro definition is available as a sub-object of a
template's <code>macros</code> object. For example, to access a macro named
<code>header</code> in a template named <code>master.html</code>, you could use the path
expression <code>master.html/macros/header</code>.</p><h3> Examples</h3>
<p> Simple macro definition:<pre> <p metal:define-macro="copyright">
Copyright 2001, <em>Foobar</em> Inc.
</p></pre>
</p><h3> See Also</h3>
<p> metal:use-macro</p><p> metal:define-slot</p><h2> define-slot: Define a macro customization point</h2>
<h3> Syntax</h3>
<p> <code>metal:define-slot</code> syntax:<pre> argument ::= Name</pre>
</p><h3> Description</h3>
<p> The <code>metal:define-slot</code> statement defines a macro customization
point or <em>slot</em>. When a macro is used, its slots can be replaced,
in order to customize the macro. Slot definitions provide default
content for the slot. You will get the default slot contents if
you decide not to customize the macro when using it.</p><p> The <code>metal:define-slot</code> statement must be used inside a
<code>metal:define-macro</code> statement.</p><p> Slot names must be unique within a macro.</p><h3> Examples</h3>
<p> Simple macro with slot:<pre> <p metal:define-macro="hello">
Hello <b metal:define-slot="name">World</b>
</p></pre>
</p><p> This example defines a macro with one slot named <code>name</code>. When you
use this macro you can customize the <code>b</code> element by filling the
<code>name</code> slot.</p><h3> See Also</h3>
<p> metal:fill-slot</p><h2> fill-slot: Customize a macro</h2>
<h3> Syntax</h3>
<p> <code>metal:fill-slot</code> syntax:<pre> argument ::= Name</pre>
</p><h3> Description</h3>
<p> The <code>metal:fill-slot</code> statement customizes a macro by replacing a
<em>slot</em> in the macro with the statement element (and its content).</p><p> The <code>metal:fill-slot</code> statement must be used inside a
<code>metal:use-macro</code> statement.</p><p> Slot names must be unique within a macro.</p><p> If the named slot does not exist within the macro, the slot
contents will be silently dropped.</p><h3> Examples</h3>
<p> Given this macro:<pre> <p metal:define-macro="hello">
Hello <b metal:define-slot="name">World</b>
</p></pre>
</p><p> You can fill the <code>name</code> slot like so:<pre> <p metal:use-macro="container/master.html/macros/hello">
Hello <b metal:fill-slot="name">Kevin Bacon</b>
</p></pre>
</p><h3> See Also</h3>
<p> metal:define-slot</p><h2> use-macro: Use a macro</h2>
<h3> Syntax</h3>
<p> <code>metal:use-macro</code> syntax:<pre> argument ::= expression</pre>
</p><h3> Description</h3>
<p> The <code>metal:use-macro</code> statement replaces the statement element
with a macro. The statement expression describes a macro
definition. </p><p> In Zope the expression will generally be a path expression
referring to a macro defined in another template. See
"metal:define-macro" for more information.</p><p> The effect of expanding a macro is to graft a subtree from another
document (or from elsewhere in the current document) in place of
the statement element, replacing the existing sub-tree. Parts of
the original subtree may remain, grafted onto the new subtree, if
the macro has <em>slots</em>. See
metal:define-slot for more information. If
the macro body uses any macros, they are expanded first.</p><p> When a macro is expanded, its <code>metal:define-macro</code> attribute is
replaced with the <code>metal:use-macro</code> attribute from the statement
element. This makes the root of the expanded macro a valid
<code>use-macro</code> statement element.</p><h3> Examples</h3>
<p> Basic macro usage:<pre> <p metal:use-macro="container/other.html/macros/header">
header macro from defined in other.html template
</p></pre>
</p><p> This example refers to the <code>header</code> macro defined in the
<code>other.html</code> template which is in the same folder as the current
template. When the macro is expanded, the <code>p</code> element and its
contents will be replaced by the macro. Note: there will still be
a <code>metal:use-macro</code> attribute on the replacement element.</p><h3> See Also</h3>
<p> metal:define-macro</p><p> metal:fill-slot</p></body>
</html>
distrib
>
Mandriva
>
2010.0
>
i586
>
media
>
contrib-release
>
by-pkgid
>
8b32d38f0094104a5fd847636983daa8
>
files
>
33
