Mercurial > babel > mirror
annotate doc/catalogs.txt @ 52:6b9c32893007 trunk
Support sub-commands in command-line interface, and renamed the generated script wrapper to `babel`. See #9.
author | cmlenz |
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date | Thu, 07 Jun 2007 22:59:25 +0000 |
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2 | 1 .. -*- mode: rst; encoding: utf-8 -*- |
2 | |
3 ============================= | |
4 Working with Message Catalogs | |
5 ============================= | |
6 | |
7 .. contents:: Contents | |
8 :depth: 2 | |
9 .. sectnum:: | |
10 | |
11 | |
12 Introduction | |
13 ============ | |
14 | |
15 The ``gettext`` translation system enables you to mark any strings used in your | |
16 application as subject to localization, by wrapping them in functions such as | |
17 ``gettext(str)`` and ``ngettext(singular, plural, num)``. For brevity, the | |
40 | 18 ``gettext`` function is often aliased to ``_(str)``, so you can write: |
19 | |
20 .. code-block:: python | |
2 | 21 |
22 print _("Hello") | |
23 | |
40 | 24 instead of just: |
25 | |
26 .. code-block:: python | |
2 | 27 |
28 print "Hello" | |
29 | |
30 to make the string "Hello" localizable. | |
31 | |
32 Message catalogs are collections of translations for such localizable messages | |
33 used in an application. They are commonly stored in PO (Portable Object) and MO | |
34 (Machine Object) files, the formats of which are defined by the GNU `gettext`_ | |
35 tools and the GNU `translation project`_. | |
36 | |
37 .. _`gettext`: http://www.gnu.org/software/gettext/ | |
38 .. _`translation project`: http://sourceforge.net/projects/translation | |
39 | |
40 The general procedure for building message catalogs looks something like this: | |
41 | |
42 * use a tool (such as ``xgettext``) to extract localizable strings from the | |
43 code base and write them to a POT (PO Template) file. | |
44 * make a copy of the POT file for a specific locale (for example, "en_US") | |
45 and start translating the messages | |
46 * use a tool such as ``msgfmt`` to compile the locale PO file into an binary | |
47 MO file | |
48 * later, when code changes make it necessary to update the translations, you | |
49 regenerate the POT file and merge the changes into the various | |
50 locale-specific PO files, for example using ``msgmerge`` | |
51 | |
52 Python provides the `gettext module`_ as part of the standard library, which | |
53 enables applications to work with appropriately generated MO files. | |
54 | |
55 .. _`gettext module`: http://docs.python.org/lib/module-gettext.html | |
56 | |
57 As ``gettext`` provides a solid and well supported foundation for translating | |
58 application messages, Babel does not reinvent the wheel, but rather reuses this | |
59 infrastructure, and makes it easier to build message catalogs for Python | |
60 applications. | |
61 | |
62 | |
63 Message Extraction | |
64 ================== | |
65 | |
66 Babel provides functionality similar to that of the ``xgettext`` program, | |
67 except that only extraction from Python source files is built-in, while support | |
68 for other file formats can be added using a simple extension mechanism. | |
69 | |
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70 Unlike ``xgettext``, which is usually invoked once for every file, the routines |
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71 for message extraction in Babel operate on directories. While the per-file |
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72 approach of ``xgettext`` works nicely with projects using a ``Makefile``, |
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73 Python projects rarely use ``make``, and thus a different mechanism is needed |
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74 for extracting messages from the heterogeneous collection of source files that |
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75 many Python projects are composed of. |
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76 |
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77 When message extraction is based on directories instead of individual files, |
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78 there needs to be a way to configure which files should be treated in which |
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79 manner. For example, while many projects may contain ``.html`` files, some of |
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80 those files may be static HTML files that don't contain localizable message, |
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81 while others may be `Django`_ templates, and still others may contain `Genshi`_ |
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82 markup templates. Some projects may even mix HTML files for different templates |
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83 languages (for whatever reason). Therefore the way in which messages are |
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84 extracted from source files can not only depend on the file extension, but |
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85 needs to be controllable in a precise manner. |
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86 |
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87 .. _`Django`: http://www.djangoproject.com/ |
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88 .. _`Genshi`: http://genshi.edgewall.org/ |
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89 |
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90 Babel accepts a configuration file to specify this mapping of files to |
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91 extraction methods, which is described below. |
2 | 92 |
93 | |
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94 .. _`mapping`: |
2 | 95 |
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96 ------------------------------------------- |
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97 Extraction Method Mapping and Configuration |
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98 ------------------------------------------- |
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99 |
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100 The mapping of extraction methods to files in Babel is done via a configuration |
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101 file. This file maps extended glob patterns to the names of the extraction |
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102 methods, and can also set various options for each pattern (which options are |
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103 available depends on the specific extraction method). |
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104 |
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105 For example, the following configuration adds extraction of messages from both |
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106 Genshi markup templates and text templates: |
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107 |
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108 .. code-block:: ini |
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109 |
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110 # Extraction from Python source files |
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111 |
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112 [python: foobar/**.py] |
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113 |
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114 # Extraction from Genshi HTML and text templates |
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115 |
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116 [genshi: foobar/**/templates/**.html] |
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117 ignore_tags = script,style |
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118 include_attrs = alt title summary |
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119 |
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120 [genshi: foobar/**/templates/**.txt] |
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121 template_class = genshi.template.text:TextTemplate |
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122 encoding = ISO-8819-15 |
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123 |
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124 The configuration file syntax is based on the format commonly found in ``.INI`` |
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125 files on Windows systems, and as supported by the ``ConfigParser`` module in |
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126 the Python standard libraries. Section names (the strings enclosed in square |
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127 brackets) specify both the name of the extraction method, and the extended glob |
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128 pattern to specify the files that this extraction method should be used for, |
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129 separated by a colon. The options in the sections are passed to the extraction |
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130 method. Which options are available is specific to the extraction method used. |
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131 |
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132 The extended glob patterns used in this configuration are similar to the glob |
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133 patterns provided by most shells. A single asterisk (``*``) is a wildcard for |
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134 any number of characters (except for the pathname component separator "/"), |
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135 while a question mark (``?``) only matches a single character. In addition, |
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136 two subsequent asterisk characters (``**``) can be used to make the wildcard |
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137 match any directory level, so the pattern ``**.txt`` matches any file with the |
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138 extension ``.txt`` in any directory. |
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139 |
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140 Lines that start with a ``#`` or ``;`` character are ignored and can be used |
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141 for comments. Empty lines are also ignored, too. |
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142 |
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143 .. note:: if you're performing message extraction using the command Babel |
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144 provides for integration into ``setup.py`` scripts (see below), you |
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145 can also provide this configuration in a different way, namely as a |
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146 keyword argument to the ``setup()`` function. |
2 | 147 |
148 | |
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149 ---------- |
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150 Front-Ends |
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151 ---------- |
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153 Babel provides two different front-ends to access its functionality for working |
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154 with message catalogs: |
2 | 155 |
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156 * A `Command-line interface <cmdline.html>`_, and |
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157 * `Integeration with distutils/setuptools <setup.html>`_ |
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158 |
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159 Which one you choose depends on the nature of your project. For most modern |
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160 Python projects, the distutils/setuptools integration is probably more |
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161 convenient. |
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162 |
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164 -------------------------- |
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165 Writing Extraction Methods |
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166 -------------------------- |
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167 |
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168 (TODO: write) |
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169 |
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170 |
2 | 171 |
172 Extended ``Translations`` Class | |
173 =============================== | |
174 | |
175 Many web-based applications are composed of a variety of different components | |
176 (possibly using some kind of plugin system), and some of those components may | |
177 provide their own message catalogs that need to be integrated into the larger | |
178 system. | |
179 | |
180 To support this usage pattern, Babel provides a ``Translations`` class that is | |
181 derived from the ``GNUTranslations`` class in the ``gettext`` module. This | |
182 class adds a ``merge()`` method that takes another ``Translations`` instance, | |
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183 and merges its contents into the catalog: |
2 | 184 |
40 | 185 .. code-block:: python |
186 | |
2 | 187 translations = Translations.load('main') |
188 translations.merge(Translations.load('plugin1')) |