Internationalize a Python application

(→Configure gettext Define the '_()' function)
(→Configure gettext Define the '_()' function)
 
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Ok, this is what we need to do. Let's code.
Ok, this is what we need to do. Let's code.
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== Configure gettext Define the '_()' function ==
 
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If you don't care too much about the details, just copy this [https://garage.maemo.org/plugins/ggit/browse.php/?p=mussorgsky;a=blob;f=src/i18n.py;hb=HEAD i18n.py] file in your src/ directory ('''change the APP_NAME''' variable there!), and in every .py file in your module that needs to translate any string, add these lines at the top:
 
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<source lang="python">
 
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import i18n
 
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_ = i18n.language.ugettext #use ugettext instead of getttext to avoid unicode errors
 
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</source>
 
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Done. If you are curious about what is going on there, the file has plenty of comments explaining every line.
 
== Mark strings for i18n ==
== Mark strings for i18n ==
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       self.set_title ( _("All music") )  <------- ADD THIS!
       self.set_title ( _("All music") )  <------- ADD THIS!
</source>
</source>
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== Generate template for the translators ==
 
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Create a po folder in your project (usually at the same level as src/) and run the following command from the top directory of your project. You can do this inside or outside Scratchbox, there is no difference. Don't forget to replace PROJECTNAME with the name of your project.
 
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xgettext --language=Python --keyword=_ --output=po/PROJECTNAME.pot `find . -name "*.py"`
 
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It will parse files, written in Python, looking for strings marked with the keyword (function name) '_' and saving the output in a file called '<code>po/PROJECTNAME.pot</code>'. The list of files is the last argument. I like to use "find", but you can manually put a list of files there.
 
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That command will generate the <code>.pot</code> file. Easy, isn't it?
 
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If you get the error "xgettext: Non-ASCII character at...", try to add the parameter "--from-code=UTF-8" to the command:
 
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xgettext --language=Python --keyword=_ --output=po/PROJECTNAME.pot --from-code=UTF-8 `find . -name "*.py"`
 
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== How to add translations ==
== How to add translations ==
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Just start it and generate a new catalog from the generated .pot file.
Just start it and generate a new catalog from the generated .pot file.
In the option window you can select the translated language, your name, email address and so on. This is useful, so others know who created this translation.  
In the option window you can select the translated language, your name, email address and so on. This is useful, so others know who created this translation.  
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Default charset seems to be UTF-8. For German I had to change it to iso-8859-15, else the special characters would have looked wrong on my PC as well as on the N900 itself.
 
Now you can start to translate all the text. If you modify your application and generate a new .pot file, you can easily import it. It will use all the existing translation and add the new/modified strings. If you changed the charset before like me, you will have to select it again.
Now you can start to translate all the text. If you modify your application and generate a new .pot file, you can easily import it. It will use all the existing translation and add the new/modified strings. If you changed the charset before like me, you will have to select it again.
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  "Content-Type: text/plain; charset=utf-8\n"  <--- THIS MUST BE UTF-8
  "Content-Type: text/plain; charset=utf-8\n"  <--- THIS MUST BE UTF-8
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If you don't know the locale of a language, can check [http://www.roseindia.net/tutorials/I18N/locales-list.shtml this list].
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If you don't know the locale of a language, can check [http://www.roseindia.net/tutorials/I18N/locales-list.shtml www.roseindia.net/tutorials/I18N/locales-list.shtml] or [http://people.w3.org/rishida/utils/subtags/ people.w3.org/rishida/utils/subtags].
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== Include translations in your installation ==
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Here again are several ways of doing it. I suggest to do it the automatic way as it is way easier if you have scratchbox.
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=== Automatic way ===
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If you already have the .tar.gz file, then you already have the structure with the files. Just unpack the .tar.gz file into a folder. If you have to pack it for the first time, MohammadAG has a good page about how to generate the needed files: [[User:Mohammad7410/Packaging]]
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Now you will have to add some basic lines to the debian/rules file.Under the line with "install: build" should be many lines with "<code>mkdir</code>" and "<code>cp -a</code>". After the last one of them, add those two lines:
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  #compile language files with msgfmt
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  msgfmt src/opt/PROJECTNAME/i18n/de.po --output-file debian/PROJECTNAME/opt/PROJECTNAME/i18n/de/LC_MESSAGES/PROJECTNAME.mo
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This will tell the autobuilder to generate the .mo files. You will need a line like that for every language!
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Don't forget to adapt the file paths. In the example the .mo files are in the sub folder i18n/de/LC_MESSAGES/
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=== Python way ===
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This part is more tricky, because it depends on your build system. I'll explain how it goes with the common python 'distutils' (what makes the usual ''<code>python setup.py install</code>'' command work). In distutils all the magic happens in the ''<code>setup.py</code>'' file.
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First of all, if in the previous steps you have added the <code>i18n.py</code> file to your source tree, don't forget to include it in your <code>data_files</code> list!
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Then, copy to the root folder of your project the file [https://garage.maemo.org/plugins/ggit/browse.php/?p=mussorgsky;a=blob;f=msgfmt.py;hb=HEAD msgfmt.py]. It is a program that translates the .po files into the binary .mo files that the application needs.
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In your <code>setup.py</code> file you need to add all this code. It "overloads" the default 'build' and 'install' instructions to include the translations in the process. Now in 'build' time it will generate the .mo files (using the <code>msgfmt.py</code> we added just now), and in 'install' time it will include the '<code>.mo</code>' files in the <code>data_files</code> list. The code is copied from this a [https://garage.maemo.org/plugins/ggit/browse.php/?p=mussorgsky;a=blob;f=setup.py;hb=HEAD setup.py] file.
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<source lang="python">
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from distutils.core import setup
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from distutils import cmd
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from distutils.command.install_data import install_data as _install_data
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from distutils.command.build import build as _build
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import msgfmt
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import os
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</source>
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This command compiles every <code>.po</code> file under the <code>po/</code> folder into a <code>.mo</code> (the <code>.mo</code> files will be under <code>build/locale/</code>)
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<source lang="python">
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class build_trans(cmd.Command):
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    description = 'Compile .po files into .mo files'
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    def initialize_options(self):
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        pass
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    def finalize_options(self):
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        pass
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    def run(self):
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        po_dir = os.path.join(os.path.dirname(os.curdir), 'po')
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        for path, names, filenames in os.walk(po_dir):
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            for f in filenames:
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                if f.endswith('.po'):
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                    lang = f[:len(f) - 3]
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                    src = os.path.join(path, f)
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                    dest_path = os.path.join('build', 'locale', lang, 'LC_MESSAGES')
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                    dest = os.path.join(dest_path, 'mussorgsky.mo')
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                    if not os.path.exists(dest_path):
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                        os.makedirs(dest_path)
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                    if not os.path.exists(dest):
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                        print 'Compiling %s' % src
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                        msgfmt.make(src, dest)
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                    else:
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                        src_mtime = os.stat(src)[8]
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                        dest_mtime = os.stat(dest)[8]
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                        if src_mtime > dest_mtime:
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                            print 'Compiling %s' % src
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                            msgfmt.make(src, dest)
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</source>
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Now we append the previous command to the 'build' command.
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<source lang="python">
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class build(_build):
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    sub_commands = _build.sub_commands + [('build_trans', None)]
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    def run(self):
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        _build.run(self)
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</source>
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Installation time: put every <code>.mo</code> file under <code>build/locale</code> in the <code>data_files</code> list (the list of things to be installed) and call the default 'install' operation
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<source lang="python">
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class install_data(_install_data):
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    def run(self):
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        for lang in os.listdir('build/locale/'):
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            lang_dir = os.path.join('share', 'locale', lang, 'LC_MESSAGES')
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            lang_file = os.path.join('build', 'locale', lang, 'LC_MESSAGES', 'mussorgsky.mo')
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            self.data_files.append( (lang_dir, [lang_file]) )
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        _install_data.run(self)
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</source>
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Finally, add the new commands in distutils...
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<source lang="python">
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cmdclass = {
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    'build': build,
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    'build_trans': build_trans,
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    'install_data': install_data,
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}
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</source>
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And don't forget to add this in your setup function, in the <code>setup.py</code>
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<source lang="python">
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setup(name        = 'your project',
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      ...
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    license      = 'GPL v2 or later',
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    data_files  = DATA,
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    scripts      = SCRIPTS,
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    cmdclass    = cmdclass  <----- DON'T FORGET THIS
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    )
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</source>
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Ok, now everything should be ready. If you run
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python2.5 setup.py build
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the terminal will print things like
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compiling es.po
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compiling de.po
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...
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Usually <code>dpkg-buildpackage</code> uses <code>python2.5 setup.py build</code> and <code>install</code>, so everything should work out-of-the-box with your previous package configuration.
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Feel free to complete/correct this wiki page with your own experience.
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[[Category:Internationalization]]
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[[Category:Development]]
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[[Category:HowTo]]
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[[Category:Python]]
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Latest revision as of 09:43, 4 May 2016

This page explains step by step how to add support for translations in a Python application for Maemo.

There are already some tutorials online about how to internationalize (i18n) Python applications, but I find them difficult to follow and they lack some needed code and final tricks to make everything work fine.

To support i18n we need to accomplish 5 tasks:

  1. Define correctly a function '_()' that translates strings
  2. Mark the strings in the code with that function
  3. Generate a template for the translators
  4. Add translations
  5. Include the translations in the installation

Contents

[edit] The overall process

From the source code, using a command line tool, we will generate a ".pot" file. It is plain text file containing all strings that need translation in the project. This .pot file only needs to be generated/recreated when the strings change in the code (and not in every build!). There is only one .pot file per project.

Then, from the .pot files and using another command line tool, we will generate the .po files for each language. There is one .po file per language, and it is the file that the translators need to complete. Both .pot and all .po files should be committed in the repository.

But once your program is running, it doesn't use .po files directly, but a binary (compiled) version of them: the .mo files. These .mo files must be re-created on build time (when creating the package) and installed in the right location in the system. These are generated files, so don't commit them to the repository.

From the code point of view, you just need to call few functions to tell gettext where are the translation files, what language do you want to use (usually the locale of the environment), and then it will use its implementation to find the right string.

Ok, this is what we need to do. Let's code.

[edit] Mark strings for i18n

This is one of the easiest parts. Browse the source code files that show something on the screen, and wrap the visible strings (window titles, dialog titles, notifications, labels, button labels and so on) with the '_()' function.

For example: 

# import the _() function!
import i18n
_ = i18n.language.gettext
 
class Example (hildon.StackableWindow):
 
   def __init__ (self):
       hildon.StackableWindow.__init__ (self)
       self.set_title ( _("All music") )   <------- ADD THIS!

[edit] How to add translations

Now you want to get a translation in an specific language. You need to generate a .po for it.

There are several ways to do it. I suggest to do it the easy way with poEdit:

[edit] With poEdit

Poedit is cross-platform gettext catalogs (.po files) editor. For more information, see its website http://www.poedit.net/. Just start it and generate a new catalog from the generated .pot file. In the option window you can select the translated language, your name, email address and so on. This is useful, so others know who created this translation.

Now you can start to translate all the text. If you modify your application and generate a new .pot file, you can easily import it. It will use all the existing translation and add the new/modified strings. If you changed the charset before like me, you will have to select it again. Every time you save the file, poEdit will generate a .mo file. You can use it for testing the new translation.

[edit] Manual way

Go to the po/ folder and run this command (again, inside/outside scratchbox doesn't matter): 

msginit --input=PROJECTNAME.pot --locale=LOCALE

For instance, if I want a .po file for the Spanish translation of my project Mussorgsky, I write: 

msginit --input=mussorgsky.pot --locale=es_ES

It will generate a file "es.po" and translators can/must work on that file.

IMPORTANT: by default the generated .po file declares its charset as ASCII. This means that translations with non-ascii characters will provoke an error in the program. To solve this, set the charset to 'utf-8': 

"Language-Team: Spanish\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=utf-8\n"  <--- THIS MUST BE UTF-8

If you don't know the locale of a language, can check www.roseindia.net/tutorials/I18N/locales-list.shtml or people.w3.org/rishida/utils/subtags.

Retrieved from "http://wiki.maemo.org/Internationalize_a_Python_application"