View source for Gettext

'''gettext''' is the GNU internationalization (i18n) library. It is commonly used for writing multilingual programs. The latest version is 0.17.
= Programming =
Source code is first modified to use the GNU gettext calls. This is, for most programming languages, done by wrapping strings that the user will see in the gettext function. To save on typing time, and to reduce code clutter, this function is commonly aliased to _, so that the Python code
 print 'Hello World!'
would become
 print _('Hello World!')

== in Python ==
To load the gettext function and alias it to _, include this code:
 from gettext import gettext as _

Now you're set for using gettext in your project. Simply wrap outputs from 'Output' to _('Output'). Keep in mind, that not only strings can require [http://en.wikipedia.org/wiki/Internationalization localization], but also 
* numbers, 
* time formats, 
* currencies, 
* time zones, 
* names and titles, 
* ...

== Example Application ==
Let's make up an example (test.py) for translating names and titles:
 from gettext import gettext as _
 
 title = _('Mr.')
 lastname = 'Hager'
 firstname = 'Chris'
 
 name = _('%(title)s %(lastname)s %(firstname)s') % {'title': title, 'lastname': lastname, 'firstname': firstname};
 print name;

== Comments ==
It's possible to leave a comment directed to the translator like this:
 # TRANSLATORS: Please just rearrange the 3 '%(...)s' parts as required.
 name = _('%(title)s %(lastname)s %(firstname)s') % {'title': title, 'lastname': lastname, 'firstname': firstname};

Note: When './setup.py genpot' is used in a sugar environment to generate the PO template file,
it specifies 'TRANS:' rather than 'TRANSLATORS:' as the marker for comments to translators.
So, if the software being internationalized is a python sugar activity, comments directed to the
translators should be marked with 'TRANS:' rather than 'TRANSLATORS:'.

== Building the template file ==
No we use '''xgettext''' to build a .po template file from the source code. This will be used by translators to derive local .po files.
 xgettext --add-comments=TRANSLATORS: test.py
Our newly created template file with translations (eg. messages.po) looks like this:
 #: test.py:3
 msgid "Mr."
 msgstr ""
 
 # TRANSLATORS: Please just rearrange the 3 '%(...)s' parts as required.
 #: test.py:7
 #, python-format
 msgid "%(title)s %(lastname)s %(firstname)s"
 msgstr ""
Distribute it and people can start translating.

= Translating =
We can derive a local .po file from the template using the msginit program. For a german translation we'd do this:
 msginit --locale=de --input=messages.po

This will create a file named 'de.po'. The translator needs to edit it either by hand or with tools such as [http://en.wikipedia.org/wiki/PoEdit poEdit]. When they are done, it will could like this:
 #: test.py:4
 msgid "Mr."
 msgstr "Hr."
 
 #: test.py:9
 #, python-format
 msgid "%(title)s %(lastname)s %(firstname)s"
 msgstr "%(title)s %(firstname)s %(lastname)s"

Finally, the .po files are compiled into a binary .mo file with ''msgfmt''.
 msgfmt de.po
These are now ready for distribution with the software package.

= Running =
On Unix-type systems, the user sets the environment variable LC_MESSAGES, and the program will display strings in the selected language, if there is an .mo file for it.

= Related Links =
* [http://www.gnu.org/software/gettext GNU Gettext Manual]