mirror of
				https://github.com/python/cpython.git
				synced 2025-10-31 18:28:49 +00:00 
			
		
		
		
	 e41251e864
			
		
	
	
		e41251e864
		
	
	
	
	
		
			
			svn+ssh://pythondev@svn.python.org/python/trunk ........ r62490 | benjamin.peterson | 2008-04-24 20:29:10 -0500 (Thu, 24 Apr 2008) | 2 lines reformat some documentation of classes so methods and attributes are under the class directive ........
		
			
				
	
	
		
			721 lines
		
	
	
	
		
			27 KiB
		
	
	
	
		
			ReStructuredText
		
	
	
	
	
	
			
		
		
	
	
			721 lines
		
	
	
	
		
			27 KiB
		
	
	
	
		
			ReStructuredText
		
	
	
	
	
	
| 
 | |
| :mod:`gettext` --- Multilingual internationalization services
 | |
| =============================================================
 | |
| 
 | |
| .. module:: gettext
 | |
|    :synopsis: Multilingual internationalization services.
 | |
| .. moduleauthor:: Barry A. Warsaw <barry@zope.com>
 | |
| .. sectionauthor:: Barry A. Warsaw <barry@zope.com>
 | |
| 
 | |
| 
 | |
| The :mod:`gettext` module provides internationalization (I18N) and localization
 | |
| (L10N) services for your Python modules and applications. It supports both the
 | |
| GNU ``gettext`` message catalog API and a higher level, class-based API that may
 | |
| be more appropriate for Python files.  The interface described below allows you
 | |
| to write your module and application messages in one natural language, and
 | |
| provide a catalog of translated messages for running under different natural
 | |
| languages.
 | |
| 
 | |
| Some hints on localizing your Python modules and applications are also given.
 | |
| 
 | |
| 
 | |
| GNU :program:`gettext` API
 | |
| --------------------------
 | |
| 
 | |
| The :mod:`gettext` module defines the following API, which is very similar to
 | |
| the GNU :program:`gettext` API.  If you use this API you will affect the
 | |
| translation of your entire application globally.  Often this is what you want if
 | |
| your application is monolingual, with the choice of language dependent on the
 | |
| locale of your user.  If you are localizing a Python module, or if your
 | |
| application needs to switch languages on the fly, you probably want to use the
 | |
| class-based API instead.
 | |
| 
 | |
| 
 | |
| .. function:: bindtextdomain(domain[, localedir])
 | |
| 
 | |
|    Bind the *domain* to the locale directory *localedir*.  More concretely,
 | |
|    :mod:`gettext` will look for binary :file:`.mo` files for the given domain using
 | |
|    the path (on Unix): :file:`localedir/language/LC_MESSAGES/domain.mo`, where
 | |
|    *languages* is searched for in the environment variables :envvar:`LANGUAGE`,
 | |
|    :envvar:`LC_ALL`, :envvar:`LC_MESSAGES`, and :envvar:`LANG` respectively.
 | |
| 
 | |
|    If *localedir* is omitted or ``None``, then the current binding for *domain* is
 | |
|    returned. [#]_
 | |
| 
 | |
| 
 | |
| .. function:: bind_textdomain_codeset(domain[, codeset])
 | |
| 
 | |
|    Bind the *domain* to *codeset*, changing the encoding of strings returned by the
 | |
|    :func:`gettext` family of functions. If *codeset* is omitted, then the current
 | |
|    binding is returned.
 | |
| 
 | |
| 
 | |
| .. function:: textdomain([domain])
 | |
| 
 | |
|    Change or query the current global domain.  If *domain* is ``None``, then the
 | |
|    current global domain is returned, otherwise the global domain is set to
 | |
|    *domain*, which is returned.
 | |
| 
 | |
| 
 | |
| .. function:: gettext(message)
 | |
| 
 | |
|    Return the localized translation of *message*, based on the current global
 | |
|    domain, language, and locale directory.  This function is usually aliased as
 | |
|    :func:`_` in the local namespace (see examples below).
 | |
| 
 | |
| 
 | |
| .. function:: lgettext(message)
 | |
| 
 | |
|    Equivalent to :func:`gettext`, but the translation is returned in the preferred
 | |
|    system encoding, if no other encoding was explicitly set with
 | |
|    :func:`bind_textdomain_codeset`.
 | |
| 
 | |
| 
 | |
| .. function:: dgettext(domain, message)
 | |
| 
 | |
|    Like :func:`gettext`, but look the message up in the specified *domain*.
 | |
| 
 | |
| 
 | |
| .. function:: ldgettext(domain, message)
 | |
| 
 | |
|    Equivalent to :func:`dgettext`, but the translation is returned in the preferred
 | |
|    system encoding, if no other encoding was explicitly set with
 | |
|    :func:`bind_textdomain_codeset`.
 | |
| 
 | |
| 
 | |
| .. function:: ngettext(singular, plural, n)
 | |
| 
 | |
|    Like :func:`gettext`, but consider plural forms. If a translation is found,
 | |
|    apply the plural formula to *n*, and return the resulting message (some
 | |
|    languages have more than two plural forms). If no translation is found, return
 | |
|    *singular* if *n* is 1; return *plural* otherwise.
 | |
| 
 | |
|    The Plural formula is taken from the catalog header. It is a C or Python
 | |
|    expression that has a free variable *n*; the expression evaluates to the index
 | |
|    of the plural in the catalog. See the GNU gettext documentation for the precise
 | |
|    syntax to be used in :file:`.po` files and the formulas for a variety of
 | |
|    languages.
 | |
| 
 | |
| 
 | |
| .. function:: lngettext(singular, plural, n)
 | |
| 
 | |
|    Equivalent to :func:`ngettext`, but the translation is returned in the preferred
 | |
|    system encoding, if no other encoding was explicitly set with
 | |
|    :func:`bind_textdomain_codeset`.
 | |
| 
 | |
| 
 | |
| .. function:: dngettext(domain, singular, plural, n)
 | |
| 
 | |
|    Like :func:`ngettext`, but look the message up in the specified *domain*.
 | |
| 
 | |
| 
 | |
| .. function:: ldngettext(domain, singular, plural, n)
 | |
| 
 | |
|    Equivalent to :func:`dngettext`, but the translation is returned in the
 | |
|    preferred system encoding, if no other encoding was explicitly set with
 | |
|    :func:`bind_textdomain_codeset`.
 | |
| 
 | |
| 
 | |
| Note that GNU :program:`gettext` also defines a :func:`dcgettext` method, but
 | |
| this was deemed not useful and so it is currently unimplemented.
 | |
| 
 | |
| Here's an example of typical usage for this API::
 | |
| 
 | |
|    import gettext
 | |
|    gettext.bindtextdomain('myapplication', '/path/to/my/language/directory')
 | |
|    gettext.textdomain('myapplication')
 | |
|    _ = gettext.gettext
 | |
|    # ...
 | |
|    print(_('This is a translatable string.'))
 | |
| 
 | |
| 
 | |
| Class-based API
 | |
| ---------------
 | |
| 
 | |
| The class-based API of the :mod:`gettext` module gives you more flexibility and
 | |
| greater convenience than the GNU :program:`gettext` API.  It is the recommended
 | |
| way of localizing your Python applications and modules.  :mod:`gettext` defines
 | |
| a "translations" class which implements the parsing of GNU :file:`.mo` format
 | |
| files, and has methods for returning strings. Instances of this "translations"
 | |
| class can also install themselves in the built-in namespace as the function
 | |
| :func:`_`.
 | |
| 
 | |
| 
 | |
| .. function:: find(domain[, localedir[,  languages[, all]]])
 | |
| 
 | |
|    This function implements the standard :file:`.mo` file search algorithm.  It
 | |
|    takes a *domain*, identical to what :func:`textdomain` takes.  Optional
 | |
|    *localedir* is as in :func:`bindtextdomain`  Optional *languages* is a list of
 | |
|    strings, where each string is a language code.
 | |
| 
 | |
|    If *localedir* is not given, then the default system locale directory is used.
 | |
|    [#]_  If *languages* is not given, then the following environment variables are
 | |
|    searched: :envvar:`LANGUAGE`, :envvar:`LC_ALL`, :envvar:`LC_MESSAGES`, and
 | |
|    :envvar:`LANG`.  The first one returning a non-empty value is used for the
 | |
|    *languages* variable. The environment variables should contain a colon separated
 | |
|    list of languages, which will be split on the colon to produce the expected list
 | |
|    of language code strings.
 | |
| 
 | |
|    :func:`find` then expands and normalizes the languages, and then iterates
 | |
|    through them, searching for an existing file built of these components:
 | |
| 
 | |
|    :file:`localedir/language/LC_MESSAGES/domain.mo`
 | |
| 
 | |
|    The first such file name that exists is returned by :func:`find`. If no such
 | |
|    file is found, then ``None`` is returned. If *all* is given, it returns a list
 | |
|    of all file names, in the order in which they appear in the languages list or
 | |
|    the environment variables.
 | |
| 
 | |
| 
 | |
| .. function:: translation(domain[, localedir[, languages[, class_[, fallback[, codeset]]]]])
 | |
| 
 | |
|    Return a :class:`Translations` instance based on the *domain*, *localedir*, and
 | |
|    *languages*, which are first passed to :func:`find` to get a list of the
 | |
|    associated :file:`.mo` file paths.  Instances with identical :file:`.mo` file
 | |
|    names are cached.  The actual class instantiated is either *class_* if provided,
 | |
|    otherwise :class:`GNUTranslations`.  The class's constructor must take a single
 | |
|    file object argument. If provided, *codeset* will change the charset used to
 | |
|    encode translated strings.
 | |
| 
 | |
|    If multiple files are found, later files are used as fallbacks for earlier ones.
 | |
|    To allow setting the fallback, :func:`copy.copy` is used to clone each
 | |
|    translation object from the cache; the actual instance data is still shared with
 | |
|    the cache.
 | |
| 
 | |
|    If no :file:`.mo` file is found, this function raises :exc:`IOError` if
 | |
|    *fallback* is false (which is the default), and returns a
 | |
|    :class:`NullTranslations` instance if *fallback* is true.
 | |
| 
 | |
| 
 | |
| .. function:: install(domain[, localedir[, unicode [, codeset[, names]]]])
 | |
| 
 | |
|    This installs the function :func:`_` in Python's builtin namespace, based on
 | |
|    *domain*, *localedir*, and *codeset* which are passed to the function
 | |
|    :func:`translation`.  The *unicode* flag is passed to the resulting translation
 | |
|    object's :meth:`install` method.
 | |
| 
 | |
|    For the *names* parameter, please see the description of the translation
 | |
|    object's :meth:`install` method.
 | |
| 
 | |
|    As seen below, you usually mark the strings in your application that are
 | |
|    candidates for translation, by wrapping them in a call to the :func:`_`
 | |
|    function, like this::
 | |
| 
 | |
|       print(_('This string will be translated.'))
 | |
| 
 | |
|    For convenience, you want the :func:`_` function to be installed in Python's
 | |
|    builtin namespace, so it is easily accessible in all modules of your
 | |
|    application.
 | |
| 
 | |
| 
 | |
| The :class:`NullTranslations` class
 | |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| Translation classes are what actually implement the translation of original
 | |
| source file message strings to translated message strings. The base class used
 | |
| by all translation classes is :class:`NullTranslations`; this provides the basic
 | |
| interface you can use to write your own specialized translation classes.  Here
 | |
| are the methods of :class:`NullTranslations`:
 | |
| 
 | |
| 
 | |
| .. class:: NullTranslations([fp])
 | |
| 
 | |
|    Takes an optional file object *fp*, which is ignored by the base class.
 | |
|    Initializes "protected" instance variables *_info* and *_charset* which are set
 | |
|    by derived classes, as well as *_fallback*, which is set through
 | |
|    :meth:`add_fallback`.  It then calls ``self._parse(fp)`` if *fp* is not
 | |
|    ``None``.
 | |
| 
 | |
| 
 | |
|    .. method:: _parse(fp)
 | |
| 
 | |
|       No-op'd in the base class, this method takes file object *fp*, and reads
 | |
|       the data from the file, initializing its message catalog.  If you have an
 | |
|       unsupported message catalog file format, you should override this method
 | |
|       to parse your format.
 | |
| 
 | |
| 
 | |
|    .. method:: add_fallback(fallback)
 | |
| 
 | |
|       Add *fallback* as the fallback object for the current translation
 | |
|       object. A translation object should consult the fallback if it cannot provide a
 | |
|       translation for a given message.
 | |
| 
 | |
| 
 | |
|    .. method:: gettext(message)
 | |
| 
 | |
|       If a fallback has been set, forward :meth:`gettext` to the
 | |
|       fallback. Otherwise, return the translated message.  Overridden in derived
 | |
|       classes.
 | |
| 
 | |
| 
 | |
|    .. method:: lgettext(message)
 | |
| 
 | |
|       If a fallback has been set, forward :meth:`lgettext` to the
 | |
|       fallback. Otherwise, return the translated message.  Overridden in derived
 | |
|       classes.
 | |
| 
 | |
|    .. method:: ugettext(message)
 | |
| 
 | |
|       If a fallback has been set, forward :meth:`ugettext` to the
 | |
|       fallback. Otherwise, return the translated message as a string. Overridden
 | |
|       in derived classes.
 | |
| 
 | |
| 
 | |
|    .. method:: ngettext(singular, plural, n)
 | |
| 
 | |
|       If a fallback has been set, forward :meth:`ngettext` to the
 | |
|       fallback. Otherwise, return the translated message.  Overridden in derived
 | |
|       classes.
 | |
| 
 | |
|    .. method:: lngettext(singular, plural, n)
 | |
| 
 | |
|       If a fallback has been set, forward :meth:`ngettext` to the
 | |
|       fallback. Otherwise, return the translated message.  Overridden in derived
 | |
|       classes.
 | |
| 
 | |
|    .. method:: ungettext(singular, plural, n)
 | |
| 
 | |
|       If a fallback has been set, forward :meth:`ungettext` to the fallback.
 | |
|       Otherwise, return the translated message as a string. Overridden in
 | |
|       derived classes.
 | |
| 
 | |
|    .. method:: info()
 | |
| 
 | |
|       Return the "protected" :attr:`_info` variable.
 | |
| 
 | |
| 
 | |
|    .. method:: charset()
 | |
| 
 | |
|       Return the "protected" :attr:`_charset` variable.
 | |
| 
 | |
| 
 | |
|    .. method:: output_charset()
 | |
| 
 | |
|       Return the "protected" :attr:`_output_charset` variable, which defines the
 | |
|       encoding used to return translated messages.
 | |
| 
 | |
| 
 | |
|    .. method:: set_output_charset(charset)
 | |
| 
 | |
|       Change the "protected" :attr:`_output_charset` variable, which defines the
 | |
|       encoding used to return translated messages.
 | |
| 
 | |
| 
 | |
|    .. method:: install([unicode [, names]])
 | |
| 
 | |
|       If the *unicode* flag is false, this method installs :meth:`self.gettext`
 | |
|       into the built-in namespace, binding it to ``_``.  If *unicode* is true,
 | |
|       it binds :meth:`self.ugettext` instead.  By default, *unicode* is false.
 | |
| 
 | |
|       If the *names* parameter is given, it must be a sequence containing the
 | |
|       names of functions you want to install in the builtin namespace in
 | |
|       addition to :func:`_`.  Supported names are ``'gettext'`` (bound to
 | |
|       :meth:`self.gettext` or :meth:`self.ugettext` according to the *unicode*
 | |
|       flag), ``'ngettext'`` (bound to :meth:`self.ngettext` or
 | |
|       :meth:`self.ungettext` according to the *unicode* flag), ``'lgettext'``
 | |
|       and ``'lngettext'``.
 | |
| 
 | |
|       Note that this is only one way, albeit the most convenient way, to make
 | |
|       the :func:`_` function available to your application.  Because it affects
 | |
|       the entire application globally, and specifically the built-in namespace,
 | |
|       localized modules should never install :func:`_`. Instead, they should use
 | |
|       this code to make :func:`_` available to their module::
 | |
| 
 | |
|          import gettext
 | |
|          t = gettext.translation('mymodule', ...)
 | |
|          _ = t.gettext
 | |
| 
 | |
|       This puts :func:`_` only in the module's global namespace and so only
 | |
|       affects calls within this module.
 | |
| 
 | |
| 
 | |
| The :class:`GNUTranslations` class
 | |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| The :mod:`gettext` module provides one additional class derived from
 | |
| :class:`NullTranslations`: :class:`GNUTranslations`.  This class overrides
 | |
| :meth:`_parse` to enable reading GNU :program:`gettext` format :file:`.mo` files
 | |
| in both big-endian and little-endian format. It also coerces both message ids
 | |
| and message strings to Unicode.
 | |
| 
 | |
| :class:`GNUTranslations` parses optional meta-data out of the translation
 | |
| catalog.  It is convention with GNU :program:`gettext` to include meta-data as
 | |
| the translation for the empty string.  This meta-data is in :rfc:`822`\ -style
 | |
| ``key: value`` pairs, and should contain the ``Project-Id-Version`` key.  If the
 | |
| key ``Content-Type`` is found, then the ``charset`` property is used to
 | |
| initialize the "protected" :attr:`_charset` instance variable, defaulting to
 | |
| ``None`` if not found.  If the charset encoding is specified, then all message
 | |
| ids and message strings read from the catalog are converted to Unicode using
 | |
| this encoding.  The :meth:`ugettext` method always returns a Unicode, while the
 | |
| :meth:`gettext` returns an encoded bytestring.  For the message id arguments
 | |
| of both methods, either Unicode strings or bytestrings containing only
 | |
| US-ASCII characters are acceptable.  Note that the Unicode version of the
 | |
| methods (i.e. :meth:`ugettext` and :meth:`ungettext`) are the recommended
 | |
| interface to use for internationalized Python programs.
 | |
| 
 | |
| The entire set of key/value pairs are placed into a dictionary and set as the
 | |
| "protected" :attr:`_info` instance variable.
 | |
| 
 | |
| If the :file:`.mo` file's magic number is invalid, or if other problems occur
 | |
| while reading the file, instantiating a :class:`GNUTranslations` class can raise
 | |
| :exc:`IOError`.
 | |
| 
 | |
| The following methods are overridden from the base class implementation:
 | |
| 
 | |
| 
 | |
| .. method:: GNUTranslations.gettext(message)
 | |
| 
 | |
|    Look up the *message* id in the catalog and return the corresponding message
 | |
|    string, as a bytestring encoded with the catalog's charset encoding, if
 | |
|    known.  If there is no entry in the catalog for the *message* id, and a fallback
 | |
|    has been set, the look up is forwarded to the fallback's :meth:`gettext` method.
 | |
|    Otherwise, the *message* id is returned.
 | |
| 
 | |
| 
 | |
| .. method:: GNUTranslations.lgettext(message)
 | |
| 
 | |
|    Equivalent to :meth:`gettext`, but the translation is returned in the preferred
 | |
|    system encoding, if no other encoding was explicitly set with
 | |
|    :meth:`set_output_charset`.
 | |
| 
 | |
| 
 | |
| .. method:: GNUTranslations.ugettext(message)
 | |
| 
 | |
|    Look up the *message* id in the catalog and return the corresponding message
 | |
|    string, as a string.  If there is no entry in the catalog for the
 | |
|    *message* id, and a fallback has been set, the look up is forwarded to the
 | |
|    fallback's :meth:`ugettext` method.  Otherwise, the *message* id is returned.
 | |
| 
 | |
| 
 | |
| .. method:: GNUTranslations.ngettext(singular, plural, n)
 | |
| 
 | |
|    Do a plural-forms lookup of a message id.  *singular* is used as the message id
 | |
|    for purposes of lookup in the catalog, while *n* is used to determine which
 | |
|    plural form to use.  The returned message string is a bytestring encoded with
 | |
|    the catalog's charset encoding, if known.
 | |
| 
 | |
|    If the message id is not found in the catalog, and a fallback is specified, the
 | |
|    request is forwarded to the fallback's :meth:`ngettext` method.  Otherwise, when
 | |
|    *n* is 1 *singular* is returned, and *plural* is returned in all other cases.
 | |
| 
 | |
| 
 | |
| .. method:: GNUTranslations.lngettext(singular, plural, n)
 | |
| 
 | |
|    Equivalent to :meth:`gettext`, but the translation is returned in the preferred
 | |
|    system encoding, if no other encoding was explicitly set with
 | |
|    :meth:`set_output_charset`.
 | |
| 
 | |
| 
 | |
| .. method:: GNUTranslations.ungettext(singular, plural, n)
 | |
| 
 | |
|    Do a plural-forms lookup of a message id.  *singular* is used as the message id
 | |
|    for purposes of lookup in the catalog, while *n* is used to determine which
 | |
|    plural form to use.  The returned message string is a string.
 | |
| 
 | |
|    If the message id is not found in the catalog, and a fallback is specified, the
 | |
|    request is forwarded to the fallback's :meth:`ungettext` method.  Otherwise,
 | |
|    when *n* is 1 *singular* is returned, and *plural* is returned in all other
 | |
|    cases.
 | |
| 
 | |
|    Here is an example::
 | |
| 
 | |
|       n = len(os.listdir('.'))
 | |
|       cat = GNUTranslations(somefile)
 | |
|       message = cat.ungettext(
 | |
|           'There is %(num)d file in this directory',
 | |
|           'There are %(num)d files in this directory',
 | |
|           n) % {'num': n}
 | |
| 
 | |
| 
 | |
| Solaris message catalog support
 | |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| The Solaris operating system defines its own binary :file:`.mo` file format, but
 | |
| since no documentation can be found on this format, it is not supported at this
 | |
| time.
 | |
| 
 | |
| 
 | |
| The Catalog constructor
 | |
| ^^^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| .. index:: single: GNOME
 | |
| 
 | |
| GNOME uses a version of the :mod:`gettext` module by James Henstridge, but this
 | |
| version has a slightly different API.  Its documented usage was::
 | |
| 
 | |
|    import gettext
 | |
|    cat = gettext.Catalog(domain, localedir)
 | |
|    _ = cat.gettext
 | |
|    print(_('hello world'))
 | |
| 
 | |
| For compatibility with this older module, the function :func:`Catalog` is an
 | |
| alias for the :func:`translation` function described above.
 | |
| 
 | |
| One difference between this module and Henstridge's: his catalog objects
 | |
| supported access through a mapping API, but this appears to be unused and so is
 | |
| not currently supported.
 | |
| 
 | |
| 
 | |
| Internationalizing your programs and modules
 | |
| --------------------------------------------
 | |
| 
 | |
| Internationalization (I18N) refers to the operation by which a program is made
 | |
| aware of multiple languages.  Localization (L10N) refers to the adaptation of
 | |
| your program, once internationalized, to the local language and cultural habits.
 | |
| In order to provide multilingual messages for your Python programs, you need to
 | |
| take the following steps:
 | |
| 
 | |
| #. prepare your program or module by specially marking translatable strings
 | |
| 
 | |
| #. run a suite of tools over your marked files to generate raw messages catalogs
 | |
| 
 | |
| #. create language specific translations of the message catalogs
 | |
| 
 | |
| #. use the :mod:`gettext` module so that message strings are properly translated
 | |
| 
 | |
| In order to prepare your code for I18N, you need to look at all the strings in
 | |
| your files.  Any string that needs to be translated should be marked by wrapping
 | |
| it in ``_('...')`` --- that is, a call to the function :func:`_`.  For example::
 | |
| 
 | |
|    filename = 'mylog.txt'
 | |
|    message = _('writing a log message')
 | |
|    fp = open(filename, 'w')
 | |
|    fp.write(message)
 | |
|    fp.close()
 | |
| 
 | |
| In this example, the string ``'writing a log message'`` is marked as a candidate
 | |
| for translation, while the strings ``'mylog.txt'`` and ``'w'`` are not.
 | |
| 
 | |
| The Python distribution comes with two tools which help you generate the message
 | |
| catalogs once you've prepared your source code.  These may or may not be
 | |
| available from a binary distribution, but they can be found in a source
 | |
| distribution, in the :file:`Tools/i18n` directory.
 | |
| 
 | |
| The :program:`pygettext` [#]_ program scans all your Python source code looking
 | |
| for the strings you previously marked as translatable.  It is similar to the GNU
 | |
| :program:`gettext` program except that it understands all the intricacies of
 | |
| Python source code, but knows nothing about C or C++ source code.  You don't
 | |
| need GNU ``gettext`` unless you're also going to be translating C code (such as
 | |
| C extension modules).
 | |
| 
 | |
| :program:`pygettext` generates textual Uniforum-style human readable message
 | |
| catalog :file:`.pot` files, essentially structured human readable files which
 | |
| contain every marked string in the source code, along with a placeholder for the
 | |
| translation strings. :program:`pygettext` is a command line script that supports
 | |
| a similar command line interface as :program:`xgettext`; for details on its use,
 | |
| run::
 | |
| 
 | |
|    pygettext.py --help
 | |
| 
 | |
| Copies of these :file:`.pot` files are then handed over to the individual human
 | |
| translators who write language-specific versions for every supported natural
 | |
| language.  They send you back the filled in language-specific versions as a
 | |
| :file:`.po` file.  Using the :program:`msgfmt.py` [#]_ program (in the
 | |
| :file:`Tools/i18n` directory), you take the :file:`.po` files from your
 | |
| translators and generate the machine-readable :file:`.mo` binary catalog files.
 | |
| The :file:`.mo` files are what the :mod:`gettext` module uses for the actual
 | |
| translation processing during run-time.
 | |
| 
 | |
| How you use the :mod:`gettext` module in your code depends on whether you are
 | |
| internationalizing a single module or your entire application. The next two
 | |
| sections will discuss each case.
 | |
| 
 | |
| 
 | |
| Localizing your module
 | |
| ^^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| If you are localizing your module, you must take care not to make global
 | |
| changes, e.g. to the built-in namespace.  You should not use the GNU ``gettext``
 | |
| API but instead the class-based API.
 | |
| 
 | |
| Let's say your module is called "spam" and the module's various natural language
 | |
| translation :file:`.mo` files reside in :file:`/usr/share/locale` in GNU
 | |
| :program:`gettext` format.  Here's what you would put at the top of your
 | |
| module::
 | |
| 
 | |
|    import gettext
 | |
|    t = gettext.translation('spam', '/usr/share/locale')
 | |
|    _ = t.lgettext
 | |
| 
 | |
| If your translators were providing you with Unicode strings in their :file:`.po`
 | |
| files, you'd instead do::
 | |
| 
 | |
|    import gettext
 | |
|    t = gettext.translation('spam', '/usr/share/locale')
 | |
|    _ = t.ugettext
 | |
| 
 | |
| 
 | |
| Localizing your application
 | |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| If you are localizing your application, you can install the :func:`_` function
 | |
| globally into the built-in namespace, usually in the main driver file of your
 | |
| application.  This will let all your application-specific files just use
 | |
| ``_('...')`` without having to explicitly install it in each file.
 | |
| 
 | |
| In the simple case then, you need only add the following bit of code to the main
 | |
| driver file of your application::
 | |
| 
 | |
|    import gettext
 | |
|    gettext.install('myapplication')
 | |
| 
 | |
| If you need to set the locale directory or the *unicode* flag, you can pass
 | |
| these into the :func:`install` function::
 | |
| 
 | |
|    import gettext
 | |
|    gettext.install('myapplication', '/usr/share/locale', unicode=1)
 | |
| 
 | |
| 
 | |
| Changing languages on the fly
 | |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| If your program needs to support many languages at the same time, you may want
 | |
| to create multiple translation instances and then switch between them
 | |
| explicitly, like so::
 | |
| 
 | |
|    import gettext
 | |
| 
 | |
|    lang1 = gettext.translation('myapplication', languages=['en'])
 | |
|    lang2 = gettext.translation('myapplication', languages=['fr'])
 | |
|    lang3 = gettext.translation('myapplication', languages=['de'])
 | |
| 
 | |
|    # start by using language1
 | |
|    lang1.install()
 | |
| 
 | |
|    # ... time goes by, user selects language 2
 | |
|    lang2.install()
 | |
| 
 | |
|    # ... more time goes by, user selects language 3
 | |
|    lang3.install()
 | |
| 
 | |
| 
 | |
| Deferred translations
 | |
| ^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| In most coding situations, strings are translated where they are coded.
 | |
| Occasionally however, you need to mark strings for translation, but defer actual
 | |
| translation until later.  A classic example is::
 | |
| 
 | |
|    animals = ['mollusk',
 | |
|               'albatross',
 | |
|    	   'rat',
 | |
|    	   'penguin',
 | |
|    	   'python',
 | |
|    	   ]
 | |
|    # ...
 | |
|    for a in animals:
 | |
|        print(a)
 | |
| 
 | |
| Here, you want to mark the strings in the ``animals`` list as being
 | |
| translatable, but you don't actually want to translate them until they are
 | |
| printed.
 | |
| 
 | |
| Here is one way you can handle this situation::
 | |
| 
 | |
|    def _(message): return message
 | |
| 
 | |
|    animals = [_('mollusk'),
 | |
|               _('albatross'),
 | |
|    	   _('rat'),
 | |
|    	   _('penguin'),
 | |
|    	   _('python'),
 | |
|    	   ]
 | |
| 
 | |
|    del _
 | |
| 
 | |
|    # ...
 | |
|    for a in animals:
 | |
|        print(_(a))
 | |
| 
 | |
| This works because the dummy definition of :func:`_` simply returns the string
 | |
| unchanged.  And this dummy definition will temporarily override any definition
 | |
| of :func:`_` in the built-in namespace (until the :keyword:`del` command). Take
 | |
| care, though if you have a previous definition of :func:`_` in the local
 | |
| namespace.
 | |
| 
 | |
| Note that the second use of :func:`_` will not identify "a" as being
 | |
| translatable to the :program:`pygettext` program, since it is not a string.
 | |
| 
 | |
| Another way to handle this is with the following example::
 | |
| 
 | |
|    def N_(message): return message
 | |
| 
 | |
|    animals = [N_('mollusk'),
 | |
|               N_('albatross'),
 | |
|    	   N_('rat'),
 | |
|    	   N_('penguin'),
 | |
|    	   N_('python'),
 | |
|    	   ]
 | |
| 
 | |
|    # ...
 | |
|    for a in animals:
 | |
|        print(_(a))
 | |
| 
 | |
| In this case, you are marking translatable strings with the function :func:`N_`,
 | |
| [#]_ which won't conflict with any definition of :func:`_`.  However, you will
 | |
| need to teach your message extraction program to look for translatable strings
 | |
| marked with :func:`N_`. :program:`pygettext` and :program:`xpot` both support
 | |
| this through the use of command line switches.
 | |
| 
 | |
| 
 | |
| :func:`gettext` vs. :func:`lgettext`
 | |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 | |
| 
 | |
| In Python 2.4 the :func:`lgettext` family of functions were introduced. The
 | |
| intention of these functions is to provide an alternative which is more
 | |
| compliant with the current implementation of GNU gettext. Unlike
 | |
| :func:`gettext`, which returns strings encoded with the same codeset used in the
 | |
| translation file, :func:`lgettext` will return strings encoded with the
 | |
| preferred system encoding, as returned by :func:`locale.getpreferredencoding`.
 | |
| Also notice that Python 2.4 introduces new functions to explicitly choose the
 | |
| codeset used in translated strings. If a codeset is explicitly set, even
 | |
| :func:`lgettext` will return translated strings in the requested codeset, as
 | |
| would be expected in the GNU gettext implementation.
 | |
| 
 | |
| 
 | |
| Acknowledgements
 | |
| ----------------
 | |
| 
 | |
| The following people contributed code, feedback, design suggestions, previous
 | |
| implementations, and valuable experience to the creation of this module:
 | |
| 
 | |
| * Peter Funk
 | |
| 
 | |
| * James Henstridge
 | |
| 
 | |
| * Juan David Ibáñez Palomar
 | |
| 
 | |
| * Marc-André Lemburg
 | |
| 
 | |
| * Martin von Löwis
 | |
| 
 | |
| * François Pinard
 | |
| 
 | |
| * Barry Warsaw
 | |
| 
 | |
| * Gustavo Niemeyer
 | |
| 
 | |
| .. rubric:: Footnotes
 | |
| 
 | |
| .. [#] The default locale directory is system dependent; for example, on RedHat Linux
 | |
|    it is :file:`/usr/share/locale`, but on Solaris it is :file:`/usr/lib/locale`.
 | |
|    The :mod:`gettext` module does not try to support these system dependent
 | |
|    defaults; instead its default is :file:`sys.prefix/share/locale`. For this
 | |
|    reason, it is always best to call :func:`bindtextdomain` with an explicit
 | |
|    absolute path at the start of your application.
 | |
| 
 | |
| .. [#] See the footnote for :func:`bindtextdomain` above.
 | |
| 
 | |
| .. [#] François Pinard has written a program called :program:`xpot` which does a
 | |
|    similar job.  It is available as part of his :program:`po-utils` package at http
 | |
|    ://po-utils.progiciels-bpi.ca/.
 | |
| 
 | |
| .. [#] :program:`msgfmt.py` is binary compatible with GNU :program:`msgfmt` except that
 | |
|    it provides a simpler, all-Python implementation.  With this and
 | |
|    :program:`pygettext.py`, you generally won't need to install the GNU
 | |
|    :program:`gettext` package to internationalize your Python applications.
 | |
| 
 | |
| .. [#] The choice of :func:`N_` here is totally arbitrary; it could have just as easily
 | |
|    been :func:`MarkThisStringForTranslation`.
 | |
| 
 |