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Documentation/0.4.x/text-templates.html

Version 1 (modified by cmlenz, 7 years ago)

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Genshi Text Template Language

In addition to the XML-based template language, Genshi provides a simple text-based template language, intended for basic plain text generation needs. The language is similar to Cheetah or Velocity.

This document describes the template language and will be most useful as reference to those developing Genshi text templates. Templates are text files of some kind that include processing directives that affect how the template is rendered, and template expressions that are dynamically substituted by variable data.

See Genshi Templating Basics for general information on embedding Python code in templates.

1   Template Directives

Directives are lines starting with a # character followed immediately by the directive name. They can affect how the template is rendered in a number of ways: Genshi provides directives for conditionals and looping, among others.

Directives must be on separate lines, and the # character must be be the first non-whitespace character on that line. Each directive must be “closed” using a #end marker. You can add after the #end marker, for example to document which directive is being closed, or even the expression associated with that directive. Any text after #end (but on the same line) is ignored, and effectively treated as a comment.

If you want to include a literal # in the output, you need to escape it by prepending a backslash character (\). Note that this is not required if the # isn't immediately followed by a letter, or it isn't the first non-whitespace character on the line.

1.1   Conditional Sections

1.1.1   #if

The content is only rendered if the expression evaluates to a truth value:

#if foo
  ${bar}
#end

Given the data foo=True and bar='Hello' in the template context, this would produce:

Hello

1.1.2   #choose

The #choose directive, in combination with the directives #when and #otherwise provides advanced contional processing for rendering one of several alternatives. The first matching #when branch is rendered, or, if no #when branch matches, the #otherwise branch is be rendered.

If the #choose directive has no argument the nested #when directives will be tested for truth:

The answer is:
#choose
  #when 0 == 1
    0
  #end
  #when 1 == 1
    1
  #end
  #otherwise
    2
  #end
#end

This would produce the following output:

The answer is:
    1

If the #choose does have an argument, the nested #when directives will be tested for equality to the parent #choose value:

The answer is:
#choose 1
  #when 0
    0
  #end
  #when 1
    1
  #end
  #otherwise
    2
  #end
#end

This would produce the following output:

The answer is:
    1

1.2   Looping

1.2.1   #for

The content is repeated for every item in an iterable:

Your items:
#for item in items
  * ${item}
#end

Given items=[1, 2, 3] in the context data, this would produce:

Your items
  * 1
  * 2
  * 3

1.3   Snippet Reuse

1.3.1   #def

The #def directive can be used to create macros, i.e. snippets of template text that have a name and optionally some parameters, and that can be inserted in other places:

#def greeting(name)
  Hello, ${name}!
#end
${greeting('world')}
${greeting('everyone else')}

The above would be rendered to:

Hello, world!
Hello, everyone else!

If a macro doesn't require parameters, it can be defined as well as called without the parenthesis. For example:

#def greeting
  Hello, world!
#end
${greeting}

The above would be rendered to:

Hello, world!

1.4   Variable Binding

1.4.1   #with

The #with directive lets you assign expressions to variables, which can be used to make expressions inside the directive less verbose and more efficient. For example, if you need use the expression author.posts more than once, and that actually results in a database query, assigning the results to a variable using this directive would probably help.

For example:

Magic numbers!
#with y=7; z=x+10
  $x $y $z
#end

Given x=42 in the context data, this would produce:

Magic numbers!
  42 7 52

Note that if a variable of the same name already existed outside of the scope of the #with directive, it will not be overwritten. Instead, it will have the same value it had prior to the #with assignment. Effectively, this means that variables are immutable in Genshi.

2   Comments

Lines where the first non-whitespace characters are ## are removed from the output, and can thus be used for comments. This can be escaped using a backslash.


See also: genshi.template, Genshi XML Template Language, Documentation, GenshiRecipes