Genshi

Common errors

• TemplateSyntaxError: invalid syntax in expression "${item.error}" of "choose" directive

  cause Incorrect attribute name used in template directives, such as `py:choose error="..."` instead of `py:choose test="..."`. Python keywords used as variable names can also cause this.
  fix Consult Genshi documentation for correct directive syntax (e.g., use `test` attribute for `py:choose` and `py:when`). Avoid using Python reserved keywords as template variable names (e.g., `class`).

• AttributeError: 'NoneType' object has no attribute 'strip'

  cause This often occurs when an expression in the template attempts to call a method (like `strip()`) on a variable that is `None` or `Undefined`. This is especially common in 'strict' error handling mode.
  fix Ensure all variables accessed in the template are defined and have the expected type, or use `value_of(name, default='')` for safe access with a default value. Alternatively, configure Genshi for 'lenient' error handling, though this can mask underlying issues.

• DeprecationWarning: 'cgi' is deprecated and slated for removal in Python 3.13

  cause Your application or an underlying dependency (like Genshi's internal benchmarks in older versions) is importing or using the `cgi` module, which is being removed from the Python standard library in version 3.13.
  fix For Genshi's internal use, ensure you are on version 0.7.10 or newer. For your own code, migrate away from `cgi` to a modern web framework or a compatible third-party `legacy-cgi` package if necessary for backward compatibility.

• module '_ast' has no attribute 'Index'

  cause This error specifically occurs when running older versions of Genshi (prior to 0.7.4) on Python 3.9 or newer, due to changes in Python's internal Abstract Syntax Tree (AST) structure.
  fix Upgrade your Genshi library to version 0.7.4 or higher to ensure compatibility with Python 3.9 and later versions.

Warnings

• breaking The standard library's `cgi` module, previously used by Genshi benchmarks and potentially by users in older web contexts, is slated for removal in Python 3.13. Direct usage of `cgi` within Genshi applications will break upon upgrading to Python 3.13.
  Fix: Migrate from the `cgi` module to modern web frameworks (e.g., Flask, Django) or use a community-maintained `legacy-cgi` package if adhering to CGI.
• breaking The `element.getchildren()` method was removed from Python's standard library `xml.etree.ElementTree` in Python 3.9. Older versions of Genshi might encounter `AttributeError` if they implicitly or explicitly relied on this method.
  Fix: Upgrade Genshi to version 0.7.6 or newer, which explicitly removed the use of `element.getchildren()`. Alternatively, manually update older code to use `list(elem)` or direct iteration over elements.
• gotcha Genshi's default variable lookup mode changed from 'lenient' to 'strict' in version 0.5. In 'strict' mode, accessing an undefined variable in a template raises an `UndefinedError` immediately, instead of returning an `Undefined` object.
  Fix: Ensure all variables passed to templates are defined, or explicitly set `allow_undefined=True` when initializing `MarkupTemplate` or `TextTemplate`, or `allow_lookup_exceptions=False` when creating a `TemplateLoader` for lenient behavior.
• deprecated Genshi versions prior to 0.7.8 could emit deprecation warnings related to attempts to import `Ellipsis` and `Str` for backward compatibility with older Python versions.
  Fix: Upgrade to Genshi 0.7.8 or newer, which silences these deprecation warnings.
• gotcha Changes in Python 3.9's Abstract Syntax Tree (AST) for `slice`, `Index`, and `ExtSlice` classes could lead to template processing issues in older Genshi versions.
  Fix: Upgrade to Genshi 0.7.4 or newer, which added support for these Python 3.9 AST changes.

Install

• pip install genshi Install stable release

Imports

• MarkupTemplate

  from genshi.template import MarkupTemplate

  For XML-based templates (e.g., HTML, XHTML).
• TextTemplate

  from genshi.template import TextTemplate

  For plain text templates.
• TemplateLoader

  from genshi.template import TemplateLoader

  To load templates from files or directories, often with caching.
• Markup
  wrong:

  from genshi.template import Markup

  correct:

  from genshi import Markup

  The `Markup` class for explicit safe string creation is directly under `genshi`, not `genshi.template`.

Quickstart

This quickstart demonstrates how to create a simple HTML template using `MarkupTemplate`, pass data to it, and render the output. It showcases basic variable substitution (`py:content` and `${expression}`) and iteration (`py:for`).

from genshi.template import MarkupTemplate

# Define a simple Genshi markup template string
template_string = '''
<html xmlns:py="http://genshi.edgewall.org/">
  <head>
    <title py:content="title"></title>
  </head>
  <body>
    <p>Hello, <em py:content="name"></em>!</p>
    <ul>
      <li py:for="item in items">${item}</li>
    </ul>
  </body>
</html>
'''

# Create a MarkupTemplate object
tmpl = MarkupTemplate(template_string)

# Data to render into the template
data = {
    'title': 'Genshi Example',
    'name': 'World',
    'items': ['Apple', 'Banana', 'Cherry']
}

# Generate the output stream
stream = tmpl.generate(**data)

# Render the stream to a string
output = stream.render('html')

print(output)