6.27.2 Class-based API

The class-based API of the gettext module gives you more flexibility and greater convenience than the GNU gettext API. It is the recommended way of localizing your Python applications and modules. gettext defines a ``translations'' class which implements the parsing of GNU .mo format files, and has methods for returning either standard 8-bit strings or Unicode strings. Translations instances can also install themselves in the built-in namespace as the function _().

find( domain[, localedir[, languages[, all]]])

This function implements the standard .mo file search algorithm. It takes a domain, identical to what textdomain() takes. Optional localedir is as in 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.^6.3 If languages is not given, then the following environment variables are searched: LANGUAGE, LC_ALL, LC_MESSAGES, and 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.

find() then expands and normalizes the languages, and then iterates through them, searching for an existing file built of these components:

localedir/language/LC_MESSAGES/domain.mo

The first such file name that exists is returned by 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.

translation( domain[, localedir[, languages[, class_,[fallback]]]])

Return a Translations instance based on the domain, localedir, and languages, which are first passed to find() to get a list of the associated .mo file paths. Instances with identical .mo file names are cached. The actual class instantiated is either class_ if provided, otherwise GNUTranslations. The class's constructor must take a single file object argument.

If multiple files are found, later files are used as fallbacks for earlier ones. To allow setting the fallback, copy.copy is used to clone each translation object from the cache; the actual instance data is still shared with the cache.

If no .mo file is found, this function raises IOError if fallback is false (which is the default), and returns a NullTranslations instance if fallback is true.

install( domain[, localedir[, unicode]])

This installs the function _ in Python's builtin namespace, based on domain, and localedir which are passed to the function translation(). The unicode flag is passed to the resulting translation object's 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 _() function, like this:

print _('This string will be translated.')

For convenience, you want the _() function to be installed in Python's builtin namespace, so it is easily accessible in all modules of your application.

Footnotes

... used.^6.3: See the footnote for bindtextdomain() above.

Subsections

See About this document... for information on suggesting changes.