Expression substitution and escape filtering

Expressions can be substituted inside a template script using ${...} syntax. Additionally, evaluated output can be passed to filters using ${... | <filters> } the pipe token, where filters is comma separated value of filters to be applied in specified order.

<li #crumbs>
  <a .crumbname "${crumbsurl or '' | u }"> ${crumbsname}
  <ul :menu {color : blue}>

Behind the scenes, expression substitution is handled by plugins implementing implementing tayra.interfaces.ITayraExpression interface. While coding an expression inside a template script it is possible to target the expression for specific plugin. If an expression is coded without a target plugin then default plugin will be picked based on the configuration parameter TTLCompiler['expression.default'].

py

Evaluate the text as python expression, convert the result to string, pass them to supplied filter (if any) and then substitute the final output in html output.

@@l = [1,2,3]

## Evaluating and substituting python expression
<div> ${-py l}

Filters supported by this expression are,

u,

Assume expression result as url and quote using urllib.parse.quote().

x,

Assume text as XML, and apply escape encoding.

h,

Assume text as HTML and apply html.escape( quote=True ).

t,

Strip whitespaces before and after text using strip().

evalpy

Evaluate the text as python expression and ignore the result. In the final HTMl output the expression text will be replace with an empty string. This plugin does not support any filter methods.

@@l = [1,2,3]

## Evaluating with expression extension
${-evalpy l.append(10)}
${-evalpy l.pop(0)}
<div> ${l}

To learn how to extend expression substitution with a plugin, refer to ITayraExpression section in this article.