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1 .. -*- mode: rst; encoding: utf-8 -*-
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2
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3 =====================================
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4 Internationalization and Localization
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5 =====================================
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6
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7 Genshi provides basic supporting infrastructure for internationalizing
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8 and localizing templates. That includes functionality for extracting localizable
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9 strings from templates, as well as a template filter that can apply translations
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10 to templates as they get rendered.
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11
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12 This support is based on `gettext`_ message catalogs and the `gettext Python
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13 module`_. The extraction process can be used from the API level, or through the
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14 front-ends implemented by the `Babel`_ project, for which Genshi provides a
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15 plugin.
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16
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17 .. _`gettext`: http://www.gnu.org/software/gettext/
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18 .. _`gettext python module`: http://docs.python.org/lib/module-gettext.html
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19 .. _`babel`: http://babel.edgewall.org/
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20
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21
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22 .. contents:: Contents
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23 :depth: 2
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24 .. sectnum::
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25
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26
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27 Basics
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28 ======
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29
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30 The simplest way to internationalize and translate templates would be to wrap
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31 all localizable strings in a ``gettext()`` function call (which is often aliased
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32 to ``_()`` for brevity). In that case, no extra template filter is required.
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33
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34 .. code-block:: genshi
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35
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36 <p>${_("Hello, world!")}</p>
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37
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38 However, this approach results in significant “character noise” in templates,
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39 making them harder to read and preview.
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40
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41 The ``genshi.filters.Translator`` filter allows you to get rid of the
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42 explicit `gettext`_ function calls, so you can continue to just write:
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43
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44 .. code-block:: genshi
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45
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46 <p>Hello, world!</p>
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47
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48 This text will still be extracted and translated as if you had wrapped it in a
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49 ``_()`` call.
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50
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51 .. note:: For parameterized or pluralizable messages, you need to continue using
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52 the appropriate ``gettext`` functions.
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53
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54 You can control which tags should be ignored by this process; for example, it
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55 doesn't really make sense to translate the content of the HTML
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56 ``<script></script>`` element. Both ``<script>`` and ``<style>`` are excluded
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57 by default.
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58
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59 Attribute values can also be automatically translated. The default is to
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60 consider the attributes ``abbr``, ``alt``, ``label``, ``prompt``, ``standby``,
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61 ``summary``, and ``title``, which is a list that makes sense for HTML documents.
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62 Of course, you can tell the translator to use a different set of attribute
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63 names, or none at all.
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64
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65 In addition, you can control automatic translation in your templates using the
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66 ``xml:lang`` attribute. If the value of that attribute is a literal string, the
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67 contents and attributes of the element will be ignored:
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68
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69 .. code-block:: genshi
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70
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71 <p xml:lang="en">Hello, world!</p>
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72
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73 On the other hand, if the value of the ``xml:lang`` attribute contains a Python
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74 expression, the element contents and attributes are still considered for
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75 automatic translation:
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76
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77 .. code-block:: genshi
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78
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79 <html xml:lang="$locale">
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80 ...
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81 </html>
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82
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83
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84 Extraction
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85 ==========
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86
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87 The ``Translator`` class provides a class method called ``extract``, which is
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88 a generator yielding all localizable strings found in a template or markup
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89 stream. This includes both literal strings in text nodes and attribute values,
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90 as well as strings in ``gettext()`` calls in embedded Python code. See the API
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91 documentation for details on how to use this method directly.
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92
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93 This functionality is integrated into the message extraction framework provided
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94 by the `Babel`_ project. Babel provides a command-line interface as well as
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95 commands that can be used from ``setup.py`` scripts using `Setuptools`_ or
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96 `Distutils`_.
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97
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98 .. _`setuptools`: http://peak.telecommunity.com/DevCenter/setuptools
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99 .. _`distutils`: http://docs.python.org/dist/dist.html
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100
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101 The first thing you need to do to make Babel extract messages from Genshi
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102 templates is to let Babel know which files are Genshi templates. This is done
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103 using a “mapping configuration”, which can be stored in a configuration file,
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104 or specified directly in your ``setup.py``.
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105
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106 In a configuration file, the mapping may look like this:
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107
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108 .. code-block:: ini
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109
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110 # Python souce
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111 [python:**.py]
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112
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113 # Genshi templates
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114 [genshi:**/templates/**.html]
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115 include_attrs = title
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116
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117 [genshi:**/templates/**.txt]
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118 template_class = genshi.template.TextTemplate
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119 encoding = latin-1
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120
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121 Please consult the Babel documentation for details on configuration.
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122
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123 If all goes well, running the extraction with Babel should create a POT file
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124 containing the strings from your Genshi templates and your Python source files.
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125
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126 .. note:: Genshi currently does not support “translator comments”, i.e. text in
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127 template comments that would get added to the POT file. This support
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128 may or may not be added in future versions.
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129
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130
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131 ---------------------
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132 Configuration Options
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133 ---------------------
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134
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135 The Genshi extraction plugin for Babel supports the following options:
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136
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137 ``template_class``
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138 ------------------
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139 The concrete ``Template`` class that the file should be loaded with. Specify
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140 the package/module name and the class name, separated by a colon.
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141
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142 The default is to use ``genshi.template:MarkupTemplate``, and you'll want to
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143 set it to ``genshi.template:TextTemplate`` for `text templates`_.
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144
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145 .. _`text templates`: text-templates.html
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146
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147 ``encoding``
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148 ------------------
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149 The encoding of the template file. This is only used for text templates. The
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150 default is to assume “utf-8”.
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151
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152 ``include_attrs``
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153 ------------------
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154 Comma-separated list of attribute names that should be considered to have
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155 localizable values. Only used for markup templates.
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156
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157 ``include_tags``
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158 ------------------
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159 Comma-separated list of tag names that should be ignored. Only used for markup
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160 templates.
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161
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162
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163 Translation
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164 ===========
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165
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166 If you have prepared MO files for use with Genshi using the appropriate tools,
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167 you can access the message catalogs with the `gettext Python module`_. You'll
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168 probably want to create a ``gettext.GNUTranslations`` instance, and make the
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169 translation functions it provides available to your templates by putting them
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170 in the template context.
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171
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172 The ``Translator`` filter needs to be added to the filters of the template
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173 (applying it as a stream filter will likely not have the desired effect).
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174 Furthermore it needs to be the first filter in the list, including the internal
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175 filters that Genshi adds itself:
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176
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177 .. code-block:: python
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178
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179 from genshi.filters import Translator
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180 from genshi.template import MarkupTemplate
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181
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182 template = MarkupTemplate("...")
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183 template.filters.insert(0, Translator(translations.ugettext))
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184
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185 If you're using `TemplateLoader`, you should specify a callback function in
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186 which you add the filter:
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187
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188 .. code-block:: python
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189
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190 from genshi.filters import Translator
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191 from genshi.template import TemplateLoader
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192
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193 def template_loaded(template):
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194 template.filters.insert(0, Translator(translations.ugettext))
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195
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196 loader = TemplateLoader('templates', callback=template_loaded)
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197 template = loader.load("...")
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198
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199 This approach ensures that the filter is not added everytime the template is
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200 loaded, and thus being applied multiple times.
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201
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202
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203 Related Considerations
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204 ======================
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205
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206 If you intend to produce an application that is fully prepared for an
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207 international audience, there are a couple of other things to keep in mind:
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208
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209 -------
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210 Unicode
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211 -------
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212
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213 Use ``unicode`` internally, not encoded bytestrings. Only encode/decode where
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214 data enters or exits the system. This means that your code works with characters
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215 and not just with bytes, which is an important distinction for example when
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216 calculating the length of a piece of text. When you need to decode/encode, it's
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217 probably a good idea to use UTF-8.
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218
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219 -------------
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220 Date and Time
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221 -------------
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222
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223 If your application uses datetime information that should be displayed to users
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224 in different timezones, you should try to work with UTC (universal time)
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225 internally. Do the conversion from and to "local time" when the data enters or
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226 exits the system. Make use the Python `datetime`_ module and the third-party
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227 `pytz`_ package.
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228
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229 --------------------------
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230 Formatting and Locale Data
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231 --------------------------
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232
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233 Make sure you check out the functionality provided by the `Babel`_ project for
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234 things like number and date formatting, locale display strings, etc.
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235
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236 .. _`datetime`: http://docs.python.org/lib/module-datetime.html
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237 .. _`pytz`: http://pytz.sourceforge.net/
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