cmlenz@142: .. -*- mode: rst; encoding: utf-8 -*-
cmlenz@142: 
cmlenz@142: =============================
cmlenz@142: Working with Message Catalogs
cmlenz@142: =============================
cmlenz@142: 
cmlenz@142: .. contents:: Contents
cmlenz@142:    :depth: 2
cmlenz@142: .. sectnum::
cmlenz@142: 
cmlenz@142: 
cmlenz@142: Introduction
cmlenz@142: ============
cmlenz@142: 
cmlenz@142: The ``gettext`` translation system enables you to mark any strings used in your
cmlenz@142: application as subject to localization, by wrapping them in functions such as
cmlenz@142: ``gettext(str)`` and ``ngettext(singular, plural, num)``. For brevity, the
cmlenz@142: ``gettext`` function is often aliased to ``_(str)``, so you can write:
cmlenz@142: 
cmlenz@142: .. code-block:: python
cmlenz@142: 
cmlenz@142:     print _("Hello")
cmlenz@142: 
cmlenz@142: instead of just:
cmlenz@142: 
cmlenz@142: .. code-block:: python
cmlenz@142: 
cmlenz@142:     print "Hello"
cmlenz@142: 
cmlenz@142: to make the string "Hello" localizable.
cmlenz@142: 
cmlenz@142: Message catalogs are collections of translations for such localizable messages
cmlenz@142: used in an application. They are commonly stored in PO (Portable Object) and MO
cmlenz@142: (Machine Object) files, the formats of which are defined by the GNU `gettext`_
cmlenz@142: tools and the GNU `translation project`_.
cmlenz@142: 
cmlenz@142:  .. _`gettext`: http://www.gnu.org/software/gettext/
cmlenz@142:  .. _`translation project`: http://sourceforge.net/projects/translation
cmlenz@142: 
cmlenz@142: The general procedure for building message catalogs looks something like this:
cmlenz@142: 
cmlenz@142:  * use a tool (such as ``xgettext``) to extract localizable strings from the
cmlenz@142:    code base and write them to a POT (PO Template) file.
cmlenz@142:  * make a copy of the POT file for a specific locale (for example, "en_US")
cmlenz@142:    and start translating the messages
cmlenz@142:  * use a tool such as ``msgfmt`` to compile the locale PO file into an binary
cmlenz@142:    MO file
cmlenz@142:  * later, when code changes make it necessary to update the translations, you
cmlenz@142:    regenerate the POT file and merge the changes into the various
cmlenz@142:    locale-specific PO files, for example using ``msgmerge``
cmlenz@142: 
cmlenz@142: Python provides the `gettext module`_ as part of the standard library, which
cmlenz@142: enables applications to work with appropriately generated MO files.
cmlenz@142: 
cmlenz@142:  .. _`gettext module`: http://docs.python.org/lib/module-gettext.html
cmlenz@142: 
cmlenz@142: As ``gettext`` provides a solid and well supported foundation for translating
cmlenz@142: application messages, Babel does not reinvent the wheel, but rather reuses this
cmlenz@142: infrastructure, and makes it easier to build message catalogs for Python
cmlenz@142: applications.
cmlenz@142: 
cmlenz@142: 
cmlenz@142: Message Extraction
cmlenz@142: ==================
cmlenz@142: 
cmlenz@142: Babel provides functionality similar to that of the ``xgettext`` program,
cmlenz@142: except that only extraction from Python source files is built-in, while support
cmlenz@142: for other file formats can be added using a simple extension mechanism.
cmlenz@142: 
cmlenz@142: Unlike ``xgettext``, which is usually invoked once for every file, the routines
cmlenz@142: for message extraction in Babel operate on directories. While the per-file
cmlenz@142: approach of ``xgettext`` works nicely with projects using a ``Makefile``,
cmlenz@142: Python projects rarely use ``make``, and thus a different mechanism is needed
cmlenz@142: for extracting messages from the heterogeneous collection of source files that
cmlenz@142: many Python projects are composed of.
cmlenz@142: 
cmlenz@142: When message extraction is based on directories instead of individual files,
cmlenz@142: there needs to be a way to configure which files should be treated in which
cmlenz@142: manner. For example, while many projects may contain ``.html`` files, some of
cmlenz@142: those files may be static HTML files that don't contain localizable message,
cmlenz@142: while others may be `Django`_ templates, and still others may contain `Genshi`_
cmlenz@142: markup templates. Some projects may even mix HTML files for different templates
cmlenz@142: languages (for whatever reason). Therefore the way in which messages are
cmlenz@142: extracted from source files can not only depend on the file extension, but
cmlenz@142: needs to be controllable in a precise manner.
cmlenz@142: 
cmlenz@142: .. _`Django`: http://www.djangoproject.com/
cmlenz@142: .. _`Genshi`: http://genshi.edgewall.org/
cmlenz@142: 
cmlenz@142: Babel accepts a configuration file to specify this mapping of files to
cmlenz@142: extraction methods, which is described below.
cmlenz@142: 
cmlenz@142: 
cmlenz@142: .. _`mapping`:
cmlenz@142: 
cmlenz@142: -------------------------------------------
cmlenz@142: Extraction Method Mapping and Configuration
cmlenz@142: -------------------------------------------
cmlenz@142: 
cmlenz@142: The mapping of extraction methods to files in Babel is done via a configuration
cmlenz@142: file. This file maps extended glob patterns to the names of the extraction
cmlenz@142: methods, and can also set various options for each pattern (which options are
cmlenz@142: available depends on the specific extraction method).
cmlenz@142: 
cmlenz@142: For example, the following configuration adds extraction of messages from both
cmlenz@142: Genshi markup templates and text templates:
cmlenz@142: 
cmlenz@142: .. code-block:: ini
cmlenz@142: 
cmlenz@142:     # Extraction from Python source files
cmlenz@142:     
cmlenz@142:     [python: foobar/**.py]
cmlenz@142:     
cmlenz@142:     # Extraction from Genshi HTML and text templates
cmlenz@142:     
cmlenz@142:     [genshi: foobar/**/templates/**.html]
cmlenz@142:     ignore_tags = script,style
cmlenz@142:     include_attrs = alt title summary
cmlenz@142:     
cmlenz@142:     [genshi: foobar/**/templates/**.txt]
cmlenz@142:     template_class = genshi.template.text:TextTemplate
cmlenz@142:     encoding = ISO-8819-15
cmlenz@142: 
cmlenz@142: The configuration file syntax is based on the format commonly found in ``.INI``
cmlenz@142: files on Windows systems, and as supported by the ``ConfigParser`` module in
cmlenz@142: the Python standard libraries. Section names (the strings enclosed in square
cmlenz@142: brackets) specify both the name of the extraction method, and the extended glob
cmlenz@142: pattern to specify the files that this extraction method should be used for,
cmlenz@142: separated by a colon. The options in the sections are passed to the extraction
cmlenz@142: method. Which options are available is specific to the extraction method used.
cmlenz@142: 
cmlenz@142: The extended glob patterns used in this configuration are similar to the glob
cmlenz@142: patterns provided by most shells. A single asterisk (``*``) is a wildcard for
cmlenz@142: any number of characters (except for the pathname component separator "/"),
cmlenz@142: while a question mark (``?``) only matches a single character. In addition,
cmlenz@142: two subsequent asterisk characters (``**``) can be used to make the wildcard
cmlenz@142: match any directory level, so the pattern ``**.txt`` matches any file with the
cmlenz@142: extension ``.txt`` in any directory.
cmlenz@142: 
cmlenz@142: Lines that start with a ``#`` or ``;`` character are ignored and can be used
cmlenz@142: for comments. Empty lines are also ignored, too.
cmlenz@142: 
cmlenz@142: .. note:: if you're performing message extraction using the command Babel
cmlenz@142:           provides for integration into ``setup.py`` scripts (see below), you
cmlenz@142:           can also provide this configuration in a different way, namely as a
cmlenz@142:           keyword argument to the ``setup()`` function.
cmlenz@142: 
cmlenz@142: 
cmlenz@142: ----------
cmlenz@142: Front-Ends
cmlenz@142: ----------
cmlenz@142: 
cmlenz@142: Babel provides two different front-ends to access its functionality for working
cmlenz@142: with message catalogs:
cmlenz@142: 
cmlenz@142:  * A `Command-line interface <cmdline.html>`_, and
cmlenz@142:  * `Integration with distutils/setuptools <setup.html>`_
cmlenz@142: 
cmlenz@142: Which one you choose depends on the nature of your project. For most modern
cmlenz@142: Python projects, the distutils/setuptools integration is probably more
cmlenz@142: convenient.
cmlenz@142: 
cmlenz@142: 
cmlenz@142: --------------------------
cmlenz@142: Writing Extraction Methods
cmlenz@142: --------------------------
cmlenz@142: 
cmlenz@142: Adding new methods for extracting localizable methods is easy. First, you'll
cmlenz@142: need to implement a function that complies with the following interface:
cmlenz@142: 
cmlenz@142: .. code-block:: python
cmlenz@142: 
cmlenz@142:     def extract_xxx(fileobj, keywords, comment_tags, options):
cmlenz@142:         """Extract messages from XXX files.
cmlenz@142:         
cmlenz@142:         :param fileobj: the file-like object the messages should be extracted
cmlenz@142:                         from
cmlenz@142:         :param keywords: a list of keywords (i.e. function names) that should
cmlenz@142:                          be recognized as translation functions
cmlenz@142:         :param comment_tags: a list of translator tags to search for and
cmlenz@142:                              include in the results
cmlenz@142:         :param options: a dictionary of additional options (optional)
cmlenz@142:         :return: an iterator over ``(lineno, funcname, message, comments)``
cmlenz@142:                  tuples
cmlenz@142:         :rtype: ``iterator``
cmlenz@142:         """
cmlenz@142: 
cmlenz@142: .. note:: Any strings in the tuples produced by this function must be either
cmlenz@142:           ``unicode`` objects, or ``str`` objects using plain ASCII characters.
cmlenz@142:           That means that if sources contain strings using other encodings, it
cmlenz@142:           is the job of the extractor implementation to do the decoding to
cmlenz@142:           ``unicode`` objects.
cmlenz@142: 
cmlenz@142: Next, you should register that function as an entry point. This requires your
cmlenz@142: ``setup.py`` script to use `setuptools`_, and your package to be installed with
cmlenz@142: the necessary metadata. If that's taken care of, add something like the
cmlenz@142: following to your ``setup.py`` script:
cmlenz@142: 
cmlenz@142: .. code-block:: python
cmlenz@142: 
cmlenz@142:     def setup(...
cmlenz@142: 
cmlenz@142:         entry_points = """
cmlenz@142:         [babel.extractors]
cmlenz@142:         xxx = your.package:extract_xxx
cmlenz@142:         """,
cmlenz@142: 
cmlenz@142: That is, add your extraction method to the entry point group
cmlenz@142: ``babel.extractors``, where the name of the entry point is the name that people
cmlenz@142: will use to reference the extraction method, and the value being the module and
cmlenz@142: the name of the function (separated by a colon) implementing the actual
cmlenz@142: extraction.
cmlenz@142: 
cmlenz@142: .. _`setuptools`: http://peak.telecommunity.com/DevCenter/setuptools
cmlenz@142: 
cmlenz@142: Comments Tags And Translator Comments Explanation
cmlenz@142: .................................................
cmlenz@142: 
cmlenz@142: First of all what are comments tags. Comments tags are excerpts of text to
cmlenz@142: search for in comments, only comments, right before the `python gettext`_
cmlenz@142: calls, as shown on the following example:
cmlenz@142: 
cmlenz@142:  .. _`python gettext`: http://docs.python.org/lib/module-gettext.html
cmlenz@142: 
cmlenz@142: .. code-block:: python
cmlenz@142: 
cmlenz@142:     # NOTE: This is a comment about `Foo Bar`
cmlenz@142:     _('Foo Bar')
cmlenz@142: 
cmlenz@142: The comments tag for the above example would be ``NOTE:``, and the translator
cmlenz@142: comment for that tag would be ``This is a comment about `Foo Bar```.
cmlenz@142: 
cmlenz@142: The resulting output in the catalog template would be something like::
cmlenz@142: 
cmlenz@142:     #. This is a comment about `Foo Bar`
cmlenz@142:     #: main.py:2
cmlenz@142:     msgid "Foo Bar"
cmlenz@142:     msgstr ""
cmlenz@142: 
cmlenz@142: Now, you might ask, why would I need that?
cmlenz@142: 
cmlenz@142: Consider this simple case; you have a menu item called “Manual”. You know what
cmlenz@142: it means, but when the translator sees this they will wonder did you mean:
cmlenz@142: 
cmlenz@142: 1. a document or help manual, or
cmlenz@142: 2. a manual process?
cmlenz@142: 
cmlenz@142: This is the simplest case where a translation comment such as
cmlenz@142: “The installation manual” helps to clarify the situation and makes a translator
cmlenz@142: more productive.
cmlenz@142: 
cmlenz@142: **More examples of the need for translation comments**
cmlenz@142: 
cmlenz@142: Real world examples are best. This is a discussion over the use of the word
cmlenz@142: “Forward” in Northern Sotho:
cmlenz@142: 
cmlenz@142: “When you go forward. You go ‘Pele’, but when you forward the document,
cmlenz@142: you ‘Fetišetša pele’. So if you just say forward, we don’t know what you are
cmlenz@142: talking about.
cmlenz@142: It is better if it's in a sentence. But in this case i think we will use ‘pele’
cmlenz@142: because on the string no. 86 and 88 there is “show previous page in history”
cmlenz@142: and “show next page in history”.
cmlenz@142: 
cmlenz@142: Were the translators guess correct? I think so, but it makes it so much easier
cmlenz@142: if they don’t need to be super `sleuths`_ as well as translators.
cmlenz@142: 
cmlenz@142:  .. _`sleuths`: http://www.thefreedictionary.com/sleuth
cmlenz@142: 
cmlenz@142: 
cmlenz@142: *Explanation Borrowed From:* `Wordforge`_
cmlenz@142: 
cmlenz@142:  .. _`Wordforge`: http://www.wordforge.org/static/translation_comments.html
cmlenz@142: 
cmlenz@142: **Note**: Translator comments are currently only supported in python source
cmlenz@142: code.
cmlenz@142: