Template Attribute Language Expression Syntax

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The Template Attribute Language Expression Syntax ( TALES ) describes the syntax for evaluating the expressions used by the Template Attribute Language (TAL) and Macro Expansion Template Attribute Language (METAL) for attribute values. The option of using a syntax other than TALES for this is expressly provided; as a rule, however, TALES is not replaced, but expanded.

The web application server Zope extends the TALES specification within the scope of the Zope page templates .

overview

TALES provides several methods for formulating expressions that can be used in TAL and METAL attributes and are distinguished by an (optional) prefix:

Expressions

Path expression
Prefix path:(optional, and therefore almost always left out): for access to structured variables, file system objects, macros (METAL) etc.
String expression
Prefix string:; allows path expressions in${...}
Logical negation
Prefix not:; evaluates the rest of the expression and returns its logical negation
Python expression
Prefix python:; if implemented, returns the value of the following Python expression. This is usually only used when path expressions are insufficient, e.g. B. when a function has to be called with certain arguments.
Suppression of quoting
The preceding keyword structure( without a colon) suppresses the otherwise automatically applied HTML quoting, for example to generate a complete HTML element.

Built-in names

nothing
a "non-value" that cannot be a character string , e.g. B. None ( Python programming language), void , Nil , or NULL .
options
the (named) arguments passed to the template
repeat
to access loop variables such as index , number , etc.

These names are usually supplemented with more, see Zope Page Templates .

Examples

Simple path expression for accessing a macro

<metal:form use-macro="location/page/MACROS/myform"/>

For example, here is locationthe directory that contains a template pagefile in which the macro was myformdefined. In Zope Page Templates , instead of locatione.g. B. here(as a starting point for the acquisition to search for page) or containerstand.

Loop with path, python and string expressions 

<tr tal:repeat="item python:({'key': 'eins'}, {'key': 'zwei'})">
  <td tal:content="repeat/item/number">99</td>
  <td tal:content="string:Zeile ${item/key}">Zeile 99</td>
</tr>

Output: 

<tr>
  <td>1</td>
  <td>Zeile eins</td>
</tr>
<tr>
  <td>2</td>
  <td>Zeile zwei</td>
</tr>

Explanations:

  • the tal:repeatattribute creates a variable itemand, using the Python expression, a sequence of dictionaries that is used to create multiple rows of HTML tables
  • the special loop variable (z. B. number) for itemare special, required by TALES standard variable repeatprovided
  • Path expressions can also be used within string expressions

Logical negation and TAL elements

<div tal:define="view_ok context/is_view_ok">
<tal:if condition="view_ok">
 ...
</tal:if>
<tal:else condition="not:view_ok">
 ...
</tal:else>
</div>

is_view_ok could be a method that is called from the context and checks the read authorization of the user . In the “Else branch” (which is syntactically nothing else than the “If branch”; ifand elsethere are freely chosen names that should even have been the same) the logical condition of the If branch is reversed so that only one of the two is executed becomes.

See also

Web links