i18n 0.2
Simplify the development of internationalized applications
License: BSD
Keywords: i18n gettext pybabel translation

=============================
i18n - Translations made easy
=============================

This package tries to simplify the workflow and development of
internationalized applications. It is a thin wrapper around existing tools, in
particular gettext_ and babel_.

.. _gettext: http://docs.python.org/library/gettext.html
.. _babel: http://babel.edgewall.org/


Basic usage
===========

::

    # demo.py
    #
    from i18n.translator import Translator
    supported_languages = ['it_IT', 'fr_FR', 'de_DE']
    # activate italian translations
    tr = Translator('/path/to/root', supported_languages, 'it_IT')
    print tr._('Hello world!')

where ``/path/to/root/`` is the root directory of your project. When
instantiated, the ``Translator`` class automatically creates a directory
called ``/path/to/root/languages`` where the translations are stored.

Extracting messages
===================

Before doing the actual translation, you need to **extract** the messages from
your source files, by invoking the ``extract`` command on the ``i18n`` module,
which is a wrapper around ``pybabel extract`` and ``pybabel update``::

    $ python -m i18n --root=/path/to/root --languages=it_IT,fr_FR,de_DE extract

``extract`` looks for all the messages wrapped inside calls to ``_()``,
``gettext()`` or ``ngettext()`` and produces a file called
``languages/template.pot``. This is a standard `gettext po file`` which
contains all the messages found in the application.

Moreover, ``extract()`` also creates a **message catalog** file for each of
the supported languages as ``languages/$CODE/LC_MESSAGES/messages.po``, where
``$CODE`` is one of the languages listed in ``supported_languages`` (it_IT,
fr_FR and de_DE in the example above).

The catalog files are now ready to be translated using one of the many
existing tools, for example `QT Linguist`_ or Poedit_.  For the correct
functioning of the application, the entire ``languages/`` hierarchy needs to
be preserved. We suggest to track the various ``messages.po`` files in Version
Control System together with the other files belonging to the application.

.. _`QT Linguist`: http://qt.nokia.com/products/developer-tools?currentflipperobject=cf2f1a5149cecc583f8f2733206343ca#qt-tools-at-a
.. _Poedit: http://www.poedit.net/


Updating messages
=================

During the development of the application, you will surely add new messages to
be translated. The ``extract`` command automatically handle this case: if it
finds existing catalog files, their content (including the existing
translations) is merged with the newly extracted messages.


Compiling catalogs
==================

It is necessary to compile the catalog files before using them with
gettext. By default, our ``Translator`` object automatically compiles all the
catalogs found in ``languages/``, producing the corresponding ``.mo``
files. The compilation is done only when the catalog file has been modified.
This means that in most cases you do not have to worry about the compilation
of the catalogs.

If you prefer to have more control on this step, you can pass
``autocompile=False`` to the constructor of ``Translator`` and compile them
manually from the command line::

    $ python -m i18n --root=/path/to/root --languages=it_IT,fr_FR,de_DE compile



Storing translations in a database
==================================

For some applications it is useful to let the user to define new translations
and/or override the default ones. ``i18n`` supports this use case with the
``DBTranslator`` class, which is a subclass of ``Translator``.  When
translating, ``DBTranslator`` first looks in the database: if the message is
not found, it delegates to the standard gettext behavior.

``DBTranslator`` is based on sqlalchemy_. Its constructor takes an additional
``engine`` parameter::

    from i18n.dbtranslator import DBTranslator
    from sqlalchemy import create_engine

    engine = create_engine('sqlite:///db.sqlite')
    ROOT = '/path/to/root'
    LANGUAGES = ['it_IT', 'fr_FR']
    DEST_LANGUAGE = 'it_IT'
    tr = DBTranslator(ROOT, LANGUAGES, DEST_LANGUAGE, engine=engine)
    print tr._("hello world")

``DBTranslator`` automatically creates the table ``translation_entries`` in
the DB. Then, it is up to the application to provide an user interface to
manipulate the table.  For testing, you can use the ``add_translation()``
method to insert a new translation in the DB::

    tr.add_translation("it_IT", "hello world", "ciao mondo")
    print tr._("hello world") # prints "ciao mondo"


.. _sqlalchemy: http://www.sqlalchemy.org/

How to use a global Translator
==============================

By design, ``i18n`` tries to completely avoid any global state. This means
that you can instantiate as many ``Translator`` and ``DBTranslator`` as you
want, each one referring to a different directory and/or database.  This is
especially useful for testing.

However, in practice most projects want to use a global translator which knows
about the messages of all the components in the project.  The demo application
shows a way to do it in the ``translate.py`` module::

    import py
    from i18n.translator import Translator

    # set the root of the project to the directory containing this file
    ROOT = py.path.local(__file__).dirpath()
    LANGUAGES = ['it_IT', 'fr_FR', 'de_DE']

    tr = Translator(ROOT, LANGUAGES, 'it_IT')
    _ = tr._
    ngettext = tr.ngettext

    if __name__ == '__main__':
        tr.cmdline(sys.argv)

This way, the rest of the application can simply import and use ``_()`` and
``ngettext()`` from ``translate.py``. Or, at your preference, import directly
the ``tr`` object and use ``tr._()`` and ``tr.ngettext()`` to translate
messages.

The last two lines of the code enables a convenient way to call ``extract``
and ``compile`` from the command line without having to manually specify the
root dir and the supported languages. Just run::

    $ python translate.py extract     # ...or compile

Acknowledgments
================

The development of this package has been generously funded by `S3 s.r.l.`_.

.. _`S3 s.r.l.`: http://s3srl.com/