babel/mirror: doc/messages.txt comparison

comparison doc/messages.txt @ 124:98dcabc99308 trunk

Split docs on date and number formatting.

author	cmlenz
date	Mon, 18 Jun 2007 15:15:31 +0000
parents	doc/catalogs.txt@781ee9295757
children	14fe2a8fb842

comparison

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-:31ca37101a24
+:98dcabc99308
+.. -*- mode: rst; encoding: utf-8 -*-
+=============================
+Working with Message Catalogs
+=============================
+.. contents:: Contents
+:depth: 2
+.. sectnum::
+Introduction
+============
+The ``gettext`` translation system enables you to mark any strings used in your
+application as subject to localization, by wrapping them in functions such as
+``gettext(str)`` and ``ngettext(singular, plural, num)``. For brevity, the
+``gettext`` function is often aliased to ``_(str)``, so you can write:
+.. code-block:: python
+print _("Hello")
+instead of just:
+.. code-block:: python
+print "Hello"
+to make the string "Hello" localizable.
+Message catalogs are collections of translations for such localizable messages
+used in an application. They are commonly stored in PO (Portable Object) and MO
+(Machine Object) files, the formats of which are defined by the GNU `gettext`_
+tools and the GNU `translation project`_.
+.. _`gettext`: http://www.gnu.org/software/gettext/
+.. _`translation project`: http://sourceforge.net/projects/translation
+The general procedure for building message catalogs looks something like this:
+* use a tool (such as ``xgettext``) to extract localizable strings from the
+code base and write them to a POT (PO Template) file.
+* make a copy of the POT file for a specific locale (for example, "en_US")
+and start translating the messages
+* use a tool such as ``msgfmt`` to compile the locale PO file into an binary
+MO file
+* later, when code changes make it necessary to update the translations, you
+regenerate the POT file and merge the changes into the various
+locale-specific PO files, for example using ``msgmerge``
+Python provides the `gettext module`_ as part of the standard library, which
+enables applications to work with appropriately generated MO files.
+.. _`gettext module`: http://docs.python.org/lib/module-gettext.html
+As ``gettext`` provides a solid and well supported foundation for translating
+application messages, Babel does not reinvent the wheel, but rather reuses this
+infrastructure, and makes it easier to build message catalogs for Python
+applications.
+Message Extraction
+==================
+Babel provides functionality similar to that of the ``xgettext`` program,
+except that only extraction from Python source files is built-in, while support
+for other file formats can be added using a simple extension mechanism.
+Unlike ``xgettext``, which is usually invoked once for every file, the routines
+for message extraction in Babel operate on directories. While the per-file
+approach of ``xgettext`` works nicely with projects using a ``Makefile``,
+Python projects rarely use ``make``, and thus a different mechanism is needed
+for extracting messages from the heterogeneous collection of source files that
+many Python projects are composed of.
+When message extraction is based on directories instead of individual files,
+there needs to be a way to configure which files should be treated in which
+manner. For example, while many projects may contain ``.html`` files, some of
+those files may be static HTML files that don't contain localizable message,
+while others may be `Django`_ templates, and still others may contain `Genshi`_
+markup templates. Some projects may even mix HTML files for different templates
+languages (for whatever reason). Therefore the way in which messages are
+extracted from source files can not only depend on the file extension, but
+needs to be controllable in a precise manner.
+.. _`Django`: http://www.djangoproject.com/
+.. _`Genshi`: http://genshi.edgewall.org/
+Babel accepts a configuration file to specify this mapping of files to
+extraction methods, which is described below.
+.. _`mapping`:
+-------------------------------------------
+Extraction Method Mapping and Configuration
+-------------------------------------------
+The mapping of extraction methods to files in Babel is done via a configuration
+file. This file maps extended glob patterns to the names of the extraction
+methods, and can also set various options for each pattern (which options are
+available depends on the specific extraction method).
+For example, the following configuration adds extraction of messages from both
+Genshi markup templates and text templates:
+.. code-block:: ini
+# Extraction from Python source files
+[python: foobar/**.py]
+# Extraction from Genshi HTML and text templates
+[genshi: foobar/**/templates/**.html]
+ignore_tags = script,style
+include_attrs = alt title summary
+[genshi: foobar/**/templates/**.txt]
+template_class = genshi.template.text:TextTemplate
+encoding = ISO-8819-15
+The configuration file syntax is based on the format commonly found in ``.INI``
+files on Windows systems, and as supported by the ``ConfigParser`` module in
+the Python standard libraries. Section names (the strings enclosed in square
+brackets) specify both the name of the extraction method, and the extended glob
+pattern to specify the files that this extraction method should be used for,
+separated by a colon. The options in the sections are passed to the extraction
+method. Which options are available is specific to the extraction method used.
+The extended glob patterns used in this configuration are similar to the glob
+patterns provided by most shells. A single asterisk (``*``) is a wildcard for
+any number of characters (except for the pathname component separator "/"),
+while a question mark (``?``) only matches a single character. In addition,
+two subsequent asterisk characters (``**``) can be used to make the wildcard
+match any directory level, so the pattern ``**.txt`` matches any file with the
+extension ``.txt`` in any directory.
+Lines that start with a ``#`` or ``;`` character are ignored and can be used
+for comments. Empty lines are also ignored, too.
+.. note:: if you're performing message extraction using the command Babel
+provides for integration into ``setup.py`` scripts (see below), you
+can also provide this configuration in a different way, namely as a
+keyword argument to the ``setup()`` function.
+----------
+Front-Ends
+----------
+Babel provides two different front-ends to access its functionality for working
+with message catalogs:
+* A `Command-line interface <cmdline.html>`_, and
+* `Integration with distutils/setuptools <setup.html>`_
+Which one you choose depends on the nature of your project. For most modern
+Python projects, the distutils/setuptools integration is probably more
+convenient.
+--------------------------
+Writing Extraction Methods
+--------------------------
+Adding new methods for extracting localizable methods is easy. First, you'll
+need to implement a function that complies with the following interface:
+.. code-block:: python
+def extract_xxx(fileobj, keywords, comment_tags, options):
+"""Extract messages from XXX files.
+:param fileobj: the file-like object the messages should be extracted
+from
+:param keywords: a list of keywords (i.e. function names) that should
+be recognized as translation functions
+:param comment_tags: a list of translator tags to search for and
+include in the results
+:param options: a dictionary of additional options (optional)
+:return: an iterator over ``(lineno, funcname, message, comments)``
+tuples
+:rtype: ``iterator``
+"""
+.. note:: Any strings in the tuples produced by this function must be either
+``unicode`` objects, or ``str`` objects using plain ASCII characters.
+That means that if sources contain strings using other encodings, it
+is the job of the extractor implementation to do the decoding to
+``unicode`` objects.
+Next, you should register that function as an entry point. This requires your
+``setup.py`` script to use `setuptools`_, and your package to be installed with
+the necessary metadata. If that's taken care of, add something like the
+following to your ``setup.py`` script:
+.. code-block:: python
+def setup(...
+entry_points = """
+[babel.extractors]
+xxx = your.package:extract_xxx
+""",
+That is, add your extraction method to the entry point group
+``babel.extractors``, where the name of the entry point is the name that people
+will use to reference the extraction method, and the value being the module and
+the name of the function (separated by a colon) implementing the actual
+extraction.
+.. _`setuptools`: http://peak.telecommunity.com/DevCenter/setuptools
+Comments Tags And Translator Comments Explanation
+.................................................
+First of all what are comments tags. Comments tags are excerpts of text to
+search for in comments, only comments, right before the `python gettext`_
+calls, as shown on the following example:
+.. _`python gettext`: http://docs.python.org/lib/module-gettext.html
+.. code-block:: python
+# NOTE: This is a comment about `Foo Bar`
+_('Foo Bar')
+The comments tag for the above example would be ``NOTE:``, and the translator
+comment for that tag would be ``This is a comment about `Foo Bar```.
+The resulting output in the catalog template would be something like::
+#. This is a comment about `Foo Bar`
+#: main.py:2
+msgid "Foo Bar"
+msgstr ""
+Now, you might ask, why would I need that?
+Consider this simple case; you have a menu item called “Manual”. You know what
+it means, but when the translator sees this they will wonder did you mean:
+1. a document or help manual, or
+2. a manual process?
+This is the simplest case where a translation comment such as
+“The installation manual” helps to clarify the situation and makes a translator
+more productive.
+**More examples of the need for translation comments**
+Real world examples are best. This is a discussion over the use of the word
+“Forward” in Northern Sotho:
+“When you go forward. You go ‘Pele’, but when you forward the document,
+you ‘Fetišetša pele’. So if you just say forward, we don’t know what you are
+talking about.
+It is better if it's in a sentence. But in this case i think we will use ‘pele’
+because on the string no. 86 and 88 there is “show previous page in history”
+and “show next page in history”.
+Were the translators guess correct? I think so, but it makes it so much easier
+if they don’t need to be super `sleuths`_ as well as translators.
+.. _`sleuths`: http://www.thefreedictionary.com/sleuth
+*Explanation Borrowed From:* `Wordforge`_
+.. _`Wordforge`: http://www.wordforge.org/static/translation_comments.html
+**Note**: Translator comments are currently only supported in python source
+code.

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comparison doc/messages.txt @ 124:98dcabc99308 trunk