1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
|
\section{\module{gettext} ---
Multilingual internationalization services}
\declaremodule{standard}{gettext}
\modulesynopsis{Multilingual internationalization services.}
\moduleauthor{Barry A. Warsaw}{barry@zope.com}
\sectionauthor{Barry A. Warsaw}{barry@zope.com}
The \module{gettext} module provides internationalization (I18N) and
localization (L10N) services for your Python modules and applications.
It supports both the GNU \code{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.
\subsection{GNU \program{gettext} API}
The \module{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.
\begin{funcdesc}{bindtextdomain}{domain\optional{, localedir}}
Bind the \var{domain} to the locale directory
\var{localedir}. More concretely, \module{gettext} will look for
binary \file{.mo} files for the given domain using the path (on \UNIX):
\file{\var{localedir}/\var{language}/LC_MESSAGES/\var{domain}.mo},
where \var{languages} is searched for in the environment variables
\envvar{LANGUAGE}, \envvar{LC_ALL}, \envvar{LC_MESSAGES}, and
\envvar{LANG} respectively.
If \var{localedir} is omitted or \code{None}, then the current binding
for \var{domain} is returned.\footnote{
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 \module{gettext} module
does not try to support these system dependent defaults;
instead its default is \file{\code{sys.prefix}/share/locale}.
For this reason, it is always best to call
\function{bindtextdomain()} with an explicit absolute path at
the start of your application.}
\end{funcdesc}
\begin{funcdesc}{bind_textdomain_codeset}{domain\optional{, codeset}}
Bind the \var{domain} to \var{codeset}, changing the encoding of
strings returned by the \function{gettext()} family of functions.
If \var{codeset} is omitted, then the current binding is returned.
\versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{textdomain}{\optional{domain}}
Change or query the current global domain. If \var{domain} is
\code{None}, then the current global domain is returned, otherwise the
global domain is set to \var{domain}, which is returned.
\end{funcdesc}
\begin{funcdesc}{gettext}{message}
Return the localized translation of \var{message}, based on the
current global domain, language, and locale directory. This function
is usually aliased as \function{_} in the local namespace (see
examples below).
\end{funcdesc}
\begin{funcdesc}{lgettext}{message}
Equivalent to \function{gettext()}, but the translation is returned
in the preferred system encoding, if no other encoding was explicitly
set with \function{bind_textdomain_codeset()}.
\versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{dgettext}{domain, message}
Like \function{gettext()}, but look the message up in the specified
\var{domain}.
\end{funcdesc}
\begin{funcdesc}{ldgettext}{domain, message}
Equivalent to \function{dgettext()}, but the translation is returned
in the preferred system encoding, if no other encoding was explicitly
set with \function{bind_textdomain_codeset()}.
\versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{ngettext}{singular, plural, n}
Like \function{gettext()}, but consider plural forms. If a translation
is found, apply the plural formula to \var{n}, and return the
resulting message (some languages have more than two plural forms).
If no translation is found, return \var{singular} if \var{n} is 1;
return \var{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 .po files, and the
formulas for a variety of languages.
\versionadded{2.3}
\end{funcdesc}
\begin{funcdesc}{lngettext}{singular, plural, n}
Equivalent to \function{ngettext()}, but the translation is returned
in the preferred system encoding, if no other encoding was explicitly
set with \function{bind_textdomain_codeset()}.
\versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{dngettext}{domain, singular, plural, n}
Like \function{ngettext()}, but look the message up in the specified
\var{domain}.
\versionadded{2.3}
\end{funcdesc}
\begin{funcdesc}{ldngettext}{domain, singular, plural, n}
Equivalent to \function{dngettext()}, but the translation is returned
in the preferred system encoding, if no other encoding was explicitly
set with \function{bind_textdomain_codeset()}.
\versionadded{2.4}
\end{funcdesc}
Note that GNU \program{gettext} also defines a \function{dcgettext()}
method, but this was deemed not useful and so it is currently
unimplemented.
Here's an example of typical usage for this API:
\begin{verbatim}
import gettext
gettext.bindtextdomain('myapplication', '/path/to/my/language/directory')
gettext.textdomain('myapplication')
_ = gettext.gettext
# ...
print _('This is a translatable string.')
\end{verbatim}
\subsection{Class-based API}
The class-based API of the \module{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. \module{gettext} defines a ``translations'' class which
implements the parsing of GNU \file{.mo} format files, and has methods
for returning either standard 8-bit strings or Unicode strings.
Instances of this ``translations'' class can also install themselves
in the built-in namespace as the function \function{_()}.
\begin{funcdesc}{find}{domain\optional{, localedir\optional{,
languages\optional{, all}}}}
This function implements the standard \file{.mo} file search
algorithm. It takes a \var{domain}, identical to what
\function{textdomain()} takes. Optional \var{localedir} is as in
\function{bindtextdomain()} Optional \var{languages} is a list of
strings, where each string is a language code.
If \var{localedir} is not given, then the default system locale
directory is used.\footnote{See the footnote for
\function{bindtextdomain()} above.} If \var{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 \var{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.
\function{find()} then expands and normalizes the languages, and then
iterates through them, searching for an existing file built of these
components:
\file{\var{localedir}/\var{language}/LC_MESSAGES/\var{domain}.mo}
The first such file name that exists is returned by \function{find()}.
If no such file is found, then \code{None} is returned. If \var{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.
\end{funcdesc}
\begin{funcdesc}{translation}{domain\optional{, localedir\optional{,
languages\optional{, class_\optional{,
fallback\optional{, codeset}}}}}}
Return a \class{Translations} instance based on the \var{domain},
\var{localedir}, and \var{languages}, which are first passed to
\function{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 \var{class_} if provided, otherwise
\class{GNUTranslations}. The class's constructor must take a single
file object argument. If provided, \var{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, \function{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
\exception{IOError} if \var{fallback} is false (which is the default),
and returns a \class{NullTranslations} instance if \var{fallback} is
true.
\versionchanged[Added the \var{codeset} parameter]{2.4}
\end{funcdesc}
\begin{funcdesc}{install}{domain\optional{, localedir\optional{, unicode
\optional{, codeset}}}}
This installs the function \function{_} in Python's builtin namespace,
based on \var{domain}, \var{localedir}, and \var{codeset} which are
passed to the function \function{translation()}. The \var{unicode}
flag is passed to the resulting translation object's \method{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{_()} function, like this:
\begin{verbatim}
print _('This string will be translated.')
\end{verbatim}
For convenience, you want the \function{_()} function to be installed in
Python's builtin namespace, so it is easily accessible in all modules
of your application.
\versionchanged[Added the \var{codeset} parameter]{2.4}
\end{funcdesc}
\subsubsection{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}:
\begin{methoddesc}[NullTranslations]{__init__}{\optional{fp}}
Takes an optional file object \var{fp}, which is ignored by the base
class. Initializes ``protected'' instance variables \var{_info} and
\var{_charset} which are set by derived classes, as well as \var{_fallback},
which is set through \method{add_fallback}. It then calls
\code{self._parse(fp)} if \var{fp} is not \code{None}.
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{_parse}{fp}
No-op'd in the base class, this method takes file object \var{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.
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{add_fallback}{fallback}
Add \var{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.
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{gettext}{message}
If a fallback has been set, forward \method{gettext()} to the fallback.
Otherwise, return the translated message. Overridden in derived classes.
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{lgettext}{message}
If a fallback has been set, forward \method{lgettext()} to the fallback.
Otherwise, return the translated message. Overridden in derived classes.
\versionadded{2.4}
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{ugettext}{message}
If a fallback has been set, forward \method{ugettext()} to the fallback.
Otherwise, return the translated message as a Unicode string.
Overridden in derived classes.
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{ngettext}{singular, plural, n}
If a fallback has been set, forward \method{ngettext()} to the fallback.
Otherwise, return the translated message. Overridden in derived classes.
\versionadded{2.3}
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{lngettext}{singular, plural, n}
If a fallback has been set, forward \method{ngettext()} to the fallback.
Otherwise, return the translated message. Overridden in derived classes.
\versionadded{2.4}
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{ungettext}{singular, plural, n}
If a fallback has been set, forward \method{ungettext()} to the fallback.
Otherwise, return the translated message as a Unicode string.
Overridden in derived classes.
\versionadded{2.3}
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{info}{}
Return the ``protected'' \member{_info} variable.
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{charset}{}
Return the ``protected'' \member{_charset} variable.
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{output_charset}{}
Return the ``protected'' \member{_output_charset} variable, which
defines the encoding used to return translated messages.
\versionadded{2.4}
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{set_output_charset}{charset}
Change the ``protected'' \member{_output_charset} variable, which
defines the encoding used to return translated messages.
\versionadded{2.4}
\end{methoddesc}
\begin{methoddesc}[NullTranslations]{install}{\optional{unicode}}
If the \var{unicode} flag is false, this method installs
\method{self.gettext()} into the built-in namespace, binding it to
\samp{_}. If \var{unicode} is true, it binds \method{self.ugettext()}
instead. By default, \var{unicode} is false.
Note that this is only one way, albeit the most convenient way, to
make the \function{_} function available to your application. Because it
affects the entire application globally, and specifically the built-in
namespace, localized modules should never install \function{_}.
Instead, they should use this code to make \function{_} available to
their module:
\begin{verbatim}
import gettext
t = gettext.translation('mymodule', ...)
_ = t.gettext
\end{verbatim}
This puts \function{_} only in the module's global namespace and so
only affects calls within this module.
\end{methoddesc}
\subsubsection{The \class{GNUTranslations} class}
The \module{gettext} module provides one additional class derived from
\class{NullTranslations}: \class{GNUTranslations}. This class
overrides \method{_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 \code{key: value} pairs, and should
contain the \code{Project-Id-Version} key. If the key
\code{Content-Type} is found, then the \code{charset} property is used
to initialize the ``protected'' \member{_charset} instance variable,
defaulting to \code{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
\method{ugettext()} method always returns a Unicode, while the
\method{gettext()} returns an encoded 8-bit string. For the message
id arguments of both methods, either Unicode strings or 8-bit strings
containing only US-ASCII characters are acceptable. Note that the
Unicode version of the methods (i.e. \method{ugettext()} and
\method{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'' \member{_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 \exception{IOError}.
The following methods are overridden from the base class implementation:
\begin{methoddesc}[GNUTranslations]{gettext}{message}
Look up the \var{message} id in the catalog and return the
corresponding message string, as an 8-bit string encoded with the
catalog's charset encoding, if known. If there is no entry in the
catalog for the \var{message} id, and a fallback has been set, the
look up is forwarded to the fallback's \method{gettext()} method.
Otherwise, the \var{message} id is returned.
\end{methoddesc}
\begin{methoddesc}[GNUTranslations]{lgettext}{message}
Equivalent to \method{gettext()}, but the translation is returned
in the preferred system encoding, if no other encoding was explicitly
set with \method{set_output_charset()}.
\versionadded{2.4}
\end{methoddesc}
\begin{methoddesc}[GNUTranslations]{ugettext}{message}
Look up the \var{message} id in the catalog and return the
corresponding message string, as a Unicode string. If there is no
entry in the catalog for the \var{message} id, and a fallback has been
set, the look up is forwarded to the fallback's \method{ugettext()}
method. Otherwise, the \var{message} id is returned.
\end{methoddesc}
\begin{methoddesc}[GNUTranslations]{ngettext}{singular, plural, n}
Do a plural-forms lookup of a message id. \var{singular} is used as
the message id for purposes of lookup in the catalog, while \var{n} is
used to determine which plural form to use. The returned message
string is an 8-bit string 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
\method{ngettext()} method. Otherwise, when \var{n} is 1 \var{singular} is
returned, and \var{plural} is returned in all other cases.
\versionadded{2.3}
\end{methoddesc}
\begin{methoddesc}[GNUTranslations]{lngettext}{singular, plural, n}
Equivalent to \method{gettext()}, but the translation is returned
in the preferred system encoding, if no other encoding was explicitly
set with \method{set_output_charset()}.
\versionadded{2.4}
\end{methoddesc}
\begin{methoddesc}[GNUTranslations]{ungettext}{singular, plural, n}
Do a plural-forms lookup of a message id. \var{singular} is used as
the message id for purposes of lookup in the catalog, while \var{n} is
used to determine which plural form to use. The returned message
string is a Unicode string.
If the message id is not found in the catalog, and a fallback is
specified, the request is forwarded to the fallback's
\method{ungettext()} method. Otherwise, when \var{n} is 1 \var{singular} is
returned, and \var{plural} is returned in all other cases.
Here is an example:
\begin{verbatim}
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}
\end{verbatim}
\versionadded{2.3}
\end{methoddesc}
\subsubsection{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.
\subsubsection{The Catalog constructor}
GNOME\index{GNOME} uses a version of the \module{gettext} module by
James Henstridge, but this version has a slightly different API. Its
documented usage was:
\begin{verbatim}
import gettext
cat = gettext.Catalog(domain, localedir)
_ = cat.gettext
print _('hello world')
\end{verbatim}
For compatibility with this older module, the function
\function{Catalog()} is an alias for the \function{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.
\subsection{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:
\begin{enumerate}
\item prepare your program or module by specially marking
translatable strings
\item run a suite of tools over your marked files to generate raw
messages catalogs
\item create language specific translations of the message catalogs
\item use the \module{gettext} module so that message strings are
properly translated
\end{enumerate}
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 \code{_('...')} --- that is, a call
to the function \function{_()}. For example:
\begin{verbatim}
filename = 'mylog.txt'
message = _('writing a log message')
fp = open(filename, 'w')
fp.write(message)
fp.close()
\end{verbatim}
In this example, the string \code{'writing a log message'} is marked as
a candidate for translation, while the strings \code{'mylog.txt'} and
\code{'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}\footnote{Fran\c cois 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
\url{http://www.iro.umontreal.ca/contrib/po-utils/HTML/}.} 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 \Cpp
source code. You don't need GNU \code{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:
\begin{verbatim}
pygettext.py --help
\end{verbatim}
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}\footnote{\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.} 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 \module{gettext} module uses for the actual
translation processing during run-time.
How you use the \module{gettext} module in your code depends on
whether you are internationalizing your entire application or a single
module.
\subsubsection{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 \code{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:
\begin{verbatim}
import gettext
t = gettext.translation('spam', '/usr/share/locale')
_ = t.lgettext
\end{verbatim}
If your translators were providing you with Unicode strings in their
\file{.po} files, you'd instead do:
\begin{verbatim}
import gettext
t = gettext.translation('spam', '/usr/share/locale')
_ = t.ugettext
\end{verbatim}
\subsubsection{Localizing your application}
If you are localizing your application, you can install the \function{_()}
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 \code{_('...')} 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:
\begin{verbatim}
import gettext
gettext.install('myapplication')
\end{verbatim}
If you need to set the locale directory or the \var{unicode} flag,
you can pass these into the \function{install()} function:
\begin{verbatim}
import gettext
gettext.install('myapplication', '/usr/share/locale', unicode=1)
\end{verbatim}
\subsubsection{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:
\begin{verbatim}
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()
\end{verbatim}
\subsubsection{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:
\begin{verbatim}
animals = ['mollusk',
'albatross',
'rat',
'penguin',
'python',
]
# ...
for a in animals:
print a
\end{verbatim}
Here, you want to mark the strings in the \code{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:
\begin{verbatim}
def _(message): return message
animals = [_('mollusk'),
_('albatross'),
_('rat'),
_('penguin'),
_('python'),
]
del _
# ...
for a in animals:
print _(a)
\end{verbatim}
This works because the dummy definition of \function{_()} simply returns
the string unchanged. And this dummy definition will temporarily
override any definition of \function{_()} in the built-in namespace
(until the \keyword{del} command).
Take care, though if you have a previous definition of \function{_} in
the local namespace.
Note that the second use of \function{_()} 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:
\begin{verbatim}
def N_(message): return message
animals = [N_('mollusk'),
N_('albatross'),
N_('rat'),
N_('penguin'),
N_('python'),
]
# ...
for a in animals:
print _(a)
\end{verbatim}
In this case, you are marking translatable strings with the function
\function{N_()},\footnote{The choice of \function{N_()} here is totally
arbitrary; it could have just as easily been
\function{MarkThisStringForTranslation()}.
} which won't conflict with any definition of
\function{_()}. However, you will need to teach your message extraction
program to look for translatable strings marked with \function{N_()}.
\program{pygettext} and \program{xpot} both support this through the
use of command line switches.
\subsubsection{\function{gettext()} vs. \function{lgettext()}}
In Python 2.4 the \function{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 \function{gettext()}, which
returns strings encoded with the same codeset used in the
translation file, \function{lgettext()} will return strings
encoded with the preferred system encoding, as returned by
\function{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 \function{lgettext()} will return translated strings in
the requested codeset, as would be expected in the GNU gettext
implementation.
\subsection{Acknowledgements}
The following people contributed code, feedback, design suggestions,
previous implementations, and valuable experience to the creation of
this module:
\begin{itemize}
\item Peter Funk
\item James Henstridge
\item Juan David Ib\'a\~nez Palomar
\item Marc-Andr\'e Lemburg
\item Martin von L\"owis
\item Fran\c cois Pinard
\item Barry Warsaw
\item Gustavo Niemeyer
\end{itemize}
|