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annotate doc/templates.txt @ 442:ff7c72b52fb2

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Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
author cmlenz
date Thu, 12 Apr 2007 22:40:49 +0000
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children 906b346513b6
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442
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
cmlenz
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1 .. -*- mode: rst; encoding: utf-8 -*-
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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2
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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3 ========================
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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4 Genshi Templating Basics
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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5 ========================
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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6
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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7 Genshi provides a template engine that can be used for generating either
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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8 markup (such as HTML_ or XML_) or plain text. While both share some of the
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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9 syntax (and much of the underlying implementation) they are essentially
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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10 separate languages.
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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11
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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12 .. _html: http://www.w3.org/html/
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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13 .. _xml: http://www.w3.org/XML/
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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14
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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15 This document describes the common parts of the template engine and will be most
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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16 useful as reference to those developing Genshi templates. Templates are XML or
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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17 plain text files that include processing directives_ that affect how the
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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18 template is rendered, and template expressions_ that are dynamically substituted
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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19 by variable data.
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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20
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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21
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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22 .. contents:: Contents
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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23 :depth: 3
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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24 .. sectnum::
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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25
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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26 --------
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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27 Synopsis
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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28 --------
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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29
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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30 A Genshi *markup template* is a well-formed XML document with embedded Python
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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31 used for control flow and variable substitution. Markup templates should be
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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32 used to generate any kind of HTML or XML output, as they provide many advantages
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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33 over simple text-based templates (such as automatic escaping of strings).
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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34
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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35 The following illustrates a very basic Genshi markup template::
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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36
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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37 <?python
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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38 title = "A Genshi Template"
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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39 fruits = ["apple", "orange", "kiwi"]
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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40 ?>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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41 <html xmlns:py="http://genshi.edgewall.org/">
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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42 <head>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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43 <title py:content="title">This is replaced.</title>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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44 </head>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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45
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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46 <body>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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47 <p>These are some of my favorite fruits:</p>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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48 <ul>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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49 <li py:for="fruit in fruits">
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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50 I like ${fruit}s
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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51 </li>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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52 </ul>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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53 </body>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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54 </html>
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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55
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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56 This example shows:
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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57
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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58 (a) a Python code block, using a processing instruction
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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59 (b) the Genshi namespace declaration
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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60 (c) usage of templates directives (``py:content`` and ``py:for``)
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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61 (d) an inline Python expression (``${fruit}``).
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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62
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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63 A *text template* is a simple plain text document that can also contain embedded
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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64 Python code. Text templates can be used to generate simple *non-markup* text
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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65 formats, such as the body of an plain text email. For example::
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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66
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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67 Dear $name,
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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68
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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69 These are some of my favorite fruits:
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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70 #for fruit in fruits
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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71 * $fruit
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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72 #end
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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73
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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74
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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75 ----------
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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76 Python API
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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77 ----------
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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78
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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79 The Python code required for templating with Genshi is generally based on the
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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80 following pattern:
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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81
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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82 * Attain a ``MarkupTemplate`` or ``TextTemplate`` object from a string or
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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83 file-like object containing the template source. This can either be done
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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84 directly, or through a ``TemplateLoader`` instance.
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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85 * Call the ``generate()`` method of the template, passing any data that should
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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86 be made available to the template as keyword arguments.
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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87 * Serialize the resulting stream using its ``render()`` method.
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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88
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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89 For example::
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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90
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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91 >>> from genshi.template import MarkupTemplate
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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92 >>> tmpl = MarkupTemplate('<h1>Hello, $name!</h1>')
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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93 >>> stream = tmpl.generate(name='world')
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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94 >>> print stream.render()
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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95 <h1>Hello, world!</h1>
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96
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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97 Using a text template is similar::
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98
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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99 >>> from genshi.template import TextTemplate
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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100 >>> tmpl = TextTemplate('Hello, $name!')
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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101 >>> stream = tmpl.generate(name='world')
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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102 >>> print stream.render()
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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103 Hello, world!
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104
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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105 .. note:: See the Serialization_ section of the `Markup Streams`_ page for
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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106 information on configuring template output options.
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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107
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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108 .. _serialization: streams.html#serialization
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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109 .. _`Markup Streams`: streams.html
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110
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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111 Using a template loader provides the advantage that “compiled” templates are
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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112 automatically cached, and only parsed again when the template file changes. In
ff7c72b52fb2 Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
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113 addition, it enables the use of a *template search path*, allowing template
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114 directories to be spread across different file-system locations. Using a
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115 template loader would generally look as follows::
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116
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117 from genshi.template import TemplateLoader
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118 loader = TemplateLoader([templates_dir1, templates_dir2])
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119 tmpl = loader.load('test.html')
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120 stream = tmpl.generate(title='Hello, world!')
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121 print stream.render()
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122
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123 See the `API documentation <api/index.html>`_ for details on using Genshi via
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124 the Python API.
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125
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126
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127 .. _`expressions`:
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128
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129 ------------------------------------
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130 Template Expressions and Code Blocks
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131 ------------------------------------
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132
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133 Python_ expressions can be used in text and directive arguments. An expression
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134 is substituted with the result of its evaluation against the template data.
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135 Expressions in text (which includes the values of non-directive attributes) need
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136 to prefixed with a dollar sign (``$``) and usually enclosed in curly braces
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137 (``{…}``).
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138
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139 .. _python: http://www.python.org/
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140
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141 If the expression starts with a letter and contains only letters, digits, dots,
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142 and underscores, the curly braces may be omitted. In all other cases, the
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143 braces are required so that the template processor knows where the expression
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144 ends::
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145
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146 >>> from genshi.template import MarkupTemplate
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147 >>> tmpl = MarkupTemplate('<em>${items[0].capitalize()} item</em>')
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148 >>> print tmpl.generate(items=['first', 'second'])
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149 <em>First item</em>
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150
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151 Expressions support the full power of Python. In addition, it is possible to
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152 access items in a dictionary using “dotted notation” (i.e. as if they were
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153 attributes), and vice-versa (i.e. access attributes as if they were items in a
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154 dictionary)::
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155
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156 >>> from genshi.template import MarkupTemplate
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157 >>> tmpl = MarkupTemplate('<em>${dict.foo}</em>')
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158 >>> print tmpl.generate(dict={'foo': 'bar'})
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159 <em>bar</em>
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160
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161 Because there are two ways to access either attributes or items, expressions
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162 do not raise the standard ``AttributeError`` or ``IndexError`` exceptions, but
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163 rather an exception of the type ``UndefinedError``. The same kind of error is
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164 raised when you try to access a top-level variable that is not in the context
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165 data.
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166
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167
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168 .. _`code blocks`:
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169
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170 Code Blocks
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171 ===========
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172
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173 XML templates also support full Python code blocks using the ``<?python ?>``
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174 processing instruction::
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175
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176 <div>
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177 <?python
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178 from genshi.builder import tag
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179 def greeting(name):
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180 return tag.b('Hello, %s!' % name') ?>
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181 ${greeting('world')}
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182 </div>
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183
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184 This will produce the following output::
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185
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186 <div>
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187 <b>Hello, world!</b>
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188 </div>
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189
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190 Code blocks can import modules, define classes and functions, and basically do
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191 anything you can do in normal Python code. What code blocks can *not* do is to
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192 produce content that is included directly in the generated page.
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193
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194 .. note:: Using the ``print`` statement will print to the standard output
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195 stream, just as it does for other Python code in your application.
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196
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197 This feature is not supposed to encourage mixing application code into
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198 templates, which is generally considered bad design. If you're using many code
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199 blocks, that me be a sign that you should move such code into separate Python
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200 modules.
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201
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202 .. note:: Code blocks are not currently supported in text templates.
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203
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204
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205 .. _`error handling`:
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206
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207 Error Handling
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208 ==============
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209
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210 By default, Genshi allows you to access variables that are not defined, without
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211 raising a ``NameError`` exception as regular Python code would::
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212
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213 >>> from genshi.template import MarkupTemplate
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214 >>> tmpl = MarkupTemplate('<p>${doh}</p>')
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215 >>> print tmpl.generate().render('xhtml')
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216 <p></p>
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217
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218 You *will* however get an exception if you try to call an undefined variable, or
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219 do anything else with it, such as accessing its attributes::
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220
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221 >>> from genshi.template import MarkupTemplate
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222 >>> tmpl = MarkupTemplate('<p>${doh.oops}</p>')
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223 >>> print tmpl.generate().render('xhtml')
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224 Traceback (most recent call last):
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225 ...
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226 UndefinedError: "doh" not defined
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227
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228 If you need to know whether a variable is defined, you can check its type
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229 against the ``Undefined`` class, for example in a conditional directive::
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230
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231 >>> from genshi.template import MarkupTemplate
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232 >>> tmpl = MarkupTemplate('<p>${type(doh) is not Undefined}</p>')
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233 >>> print tmpl.generate().render('xhtml')
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234 <p>False</p>
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235
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236 Alternatively, the built-in functions defined_ or value_of_ can be used in this
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237 case.
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238
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239 Strict Mode
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240 -----------
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241
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242 In addition to the default "lenient" error handling, Genshi lets you use a less
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243 forgiving mode if you prefer errors blowing up loudly instead of being ignored
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244 silently.
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245
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246 This mode can be chosen by passing the ``lookup='strict'`` keyword argument to
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247 the template initializer, or by passing the ``variable_lookup='strict'`` keyword
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248 argument to the ``TemplateLoader`` initializer::
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249
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250 >>> from genshi.template import MarkupTemplate
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251 >>> tmpl = MarkupTemplate('<p>${doh}</p>', lookup='strict')
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252 >>> print tmpl.generate().render('xhtml')
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253 Traceback (most recent call last):
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254 ...
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255 UndefinedError: "doh" not defined
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256
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257 When using strict mode, any reference to an undefined variable, as well as
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258 trying to access an non-existing item or attribute of an object, will cause an
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259 ``UndefinedError`` to be raised immediately.
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260
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261 .. note:: While this mode is currently not the default, it may be promoted to
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262 the default in future versions of Genshi. In general, the default
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263 lenient error handling mode can be considered dangerous as it silently
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264 ignores typos.
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265
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266 Custom Modes
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267 ------------
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268
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269 In addition to the built-in "lenient" and "strict" modes, it is also possible to
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270 use a custom error handling mode. For example, you could use lenient error
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271 handling in a production environment, while also logging a warning when an
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272 undefined variable is referenced.
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273
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274 See the API documentation of the ``genshi.template.eval`` module for details.
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275
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276
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277 Built-in Functions & Types
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278 ==========================
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279
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280 The following functions and types are available by default in template code, in
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281 addition to the standard built-ins that are available to all Python code.
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282
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283 .. _`defined`:
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284
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285 ``defined(name)``
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286 -----------------
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287 This function determines whether a variable of the specified name exists in
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288 the context data, and returns ``True`` if it does.
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289
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290 .. _`value_of`:
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291
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292 ``value_of(name, default=None)``
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293 --------------------------------
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294 This function returns the value of the variable with the specified name if
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295 such a variable is defined, and returns the value of the ``default``
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296 parameter if no such variable is defined.
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297
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298 .. _`Markup`:
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299
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300 ``Markup(text)``
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301 ----------------
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302 The ``Markup`` type marks a given string as being safe for inclusion in markup,
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303 meaning it will *not* be escaped in the serialization stage. Use this with care,
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304 as not escaping a user-provided string may allow malicious users to open your
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305 web site to cross-site scripting attacks.
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306
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307 .. _`Undefined`:
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308
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309 ``Undefined``
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310 ----------------
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311 The ``Undefined`` type can be used to check whether a reference variable is
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312 defined, as explained in `error handling`_.
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313
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314
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315 .. _`directives`:
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316
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317 -------------------
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318 Template Directives
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319 -------------------
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320
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321 Directives provide control flow functionality for templates, such as conditions
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322 or iteration. As the syntax for directives depends on whether you're using
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323 markup or text templates, refer to the
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324 `XML Template Language <xml-templates.html>`_ or
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325 `Text Template Language <text-templates.html>`_ pages for information.
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