Edgewall Software
Version 10 (modified by cmlenz, 8 years ago)

More on context and expressions

Markup Templates

The most important feature provided by the Markup package is a template engine.

Templates are XML files of some kind (such as XHTML) that include processing directives identified by the namespace http://markup.edgewall.org/ and template expressions that are dynamically substituted by variable data.

Table of Contents

  1. Template Context
  2. Template Expressions
  3. Template Directives
    1. py:content
    2. py:replace
    3. py:attrs
    4. py:if
    5. py:choose / py:when / py:otherwise
    6. py:for
    7. py:def
    8. py:match
  4. Template Includes

Template Context

Rendering a template boils down to applying one or more template files to some input data. This input data is represented as a Context? object in Markup. A context is basically a stack of dictionaries that manages the namespace scopes during processing: for example, some variable may be able under a given name inside a loop, but not outside of that loop.

Regardless of its stack behavior during templating processing, a context is usually initialized from a single dictionary:

>>> from markup.template import Context
>>> ctxt = Context(title='Hello, world!')
>>> print ctxt
[{'title': 'Hello, world!'}]

This data is then made available for use inside the template:

>>> from markup.template import Template
>>> tmpl = Template('<h1>$title</h1>')
>>> print tmpl.generate(ctxt)
<h1>Hello, world!</h1>

Here the title variable in the context is accessed through a template expression, discussed below.

Template Expressions

Python expressions can be used in text and attribute values. An expression is substituted with the result of its evaluation against the template data. Expressions need to prefixed with a dollar sign ($) and usually enclosed in curly braces ({…}).

If the expression starts with a letter and contains only letters and digits, the curly braces may be omitted. In all other cases, the braces are required so that the template processors knows where the expression ends:

>>> from markup.template import Context, Template
>>> tmpl = Template('<em>${items[0].capitalize()} item</em>')
>>> print tmpl.generate(Context(items=['first', 'second']))
<em>First item</em>

Expressions support the full power of Python. In addition, it is possible to:

  • access items in a dictionary using “dotted notation” (i.e. as if they were attributes)
  • access attributes using item access (i.e. as if they were items in a dictionary)
>>> from markup.template import Context, Template
>>> tmpl = Template('<em>${dict.foo}</em>')
>>> print tmpl.generate(Context(dict={'foo': 'bar'}))
<em>bar</em>

Template Directives

py:content

py:replace

py:attrs

py:if

py:choose / py:when / py:otherwise

py:for

py:def

py:match

Template Includes