gettext
--- Multilingual internationalization services¶
Source code: Lib/gettext.py
The 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 gettext API¶
The gettext
module defines the following API, which is very similar to
the GNU 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.
-
gettext.
bindtextdomain
(domain, localedir=None)¶ Bind the domain to the locale directory localedir. More concretely,
gettext
will look for binary.mo
files for the given domain using the path (on Unix):localedir/language/LC_MESSAGES/domain.mo
, where language is searched for in the environment variablesLANGUAGE
,LC_ALL
,LC_MESSAGES
, andLANG
respectively.If localedir is omitted or
None
, then the current binding for domain is returned. 1
-
gettext.
bind_textdomain_codeset
(domain, codeset=None)¶ Bind the domain to codeset, changing the encoding of byte strings returned by the
lgettext()
,ldgettext()
,lngettext()
andldngettext()
functions. If codeset is omitted, then the current binding is returned.Deprecated since version 3.8, will be removed in version 3.10.
-
gettext.
textdomain
(domain=None)¶ 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.
-
gettext.
gettext
(message)¶ Return the localized translation of message, based on the current global domain, language, and locale directory. This function is usually aliased as
_()
in the local namespace (see examples below).
-
gettext.
ngettext
(singular, plural, n)¶ Like
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
.po
files and the formulas for a variety of languages.
-
gettext.
dngettext
(domain, singular, plural, n)¶ Like
ngettext()
, but look the message up in the specified domain.
-
gettext.
pgettext
(context, message)¶
-
gettext.
dpgettext
(domain, context, message)¶
-
gettext.
npgettext
(context, singular, plural, n)¶
-
gettext.
dnpgettext
(domain, context, singular, plural, n)¶ Similar to the corresponding functions without the
p
in the prefix (that is,gettext()
,dgettext()
,ngettext()
,dngettext()
), but the translation is restricted to the given message context.Baru pada versi 3.8.
-
gettext.
lgettext
(message)¶
-
gettext.
ldgettext
(domain, message)¶
-
gettext.
lngettext
(singular, plural, n)¶
-
gettext.
ldngettext
(domain, singular, plural, n)¶ Equivalent to the corresponding functions without the
l
prefix (gettext()
,dgettext()
,ngettext()
anddngettext()
), but the translation is returned as a byte string encoded in the preferred system encoding if no other encoding was explicitly set withbind_textdomain_codeset()
.Peringatan
These functions should be avoided in Python 3, because they return encoded bytes. It's much better to use alternatives which return Unicode strings instead, since most Python applications will want to manipulate human readable text as strings instead of bytes. Further, it's possible that you may get unexpected Unicode-related exceptions if there are encoding problems with the translated strings.
Deprecated since version 3.8, will be removed in version 3.10.
Note that GNU gettext also defines a 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 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 GNUTranslations
class which implements the parsing of GNU .mo
format
files, and has methods for returning strings. Instances of this class can also
install themselves in the built-in namespace as the function _()
.
-
gettext.
find
(domain, localedir=None, languages=None, all=False)¶ This function implements the standard
.mo
file search algorithm. It takes a domain, identical to whattextdomain()
takes. Optional localedir is as inbindtextdomain()
. 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. 2 If languages is not given, then the following environment variables are searched:
LANGUAGE
,LC_ALL
,LC_MESSAGES
, andLANG
. 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, thenNone
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.
-
gettext.
translation
(domain, localedir=None, languages=None, class_=None, fallback=False, codeset=None)¶ Return a
*Translations
instance based on the domain, localedir, and languages, which are first passed tofind()
to get a list of the associated.mo
file paths. Instances with identical.mo
file names are cached. The actual class instantiated is class_ if provided, otherwiseGNUTranslations
. The class's constructor must take a single file object argument. If provided, codeset will change the charset used to encode translated strings in thelgettext()
andlngettext()
methods.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 raisesOSError
if fallback is false (which is the default), and returns aNullTranslations
instance if fallback is true.Deprecated since version 3.8, will be removed in version 3.10: The codeset parameter.
-
gettext.
install
(domain, localedir=None, codeset=None, names=None)¶ This installs the function
_()
in Python's builtins namespace, based on domain, localedir, and codeset which are passed to the functiontranslation()
.For the names parameter, please see the description of the 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 builtins namespace, so it is easily accessible in all modules of your application.Deprecated since version 3.8, will be removed in version 3.10: The codeset parameter.
The 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 NullTranslations
; this provides the basic
interface you can use to write your own specialized translation classes. Here
are the methods of NullTranslations
:
-
class
gettext.
NullTranslations
(fp=None)¶ 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
add_fallback()
. It then callsself._parse(fp)
if fp is notNone
.-
_parse
(fp)¶ No-op 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.
-
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.
-
gettext
(message)¶ If a fallback has been set, forward
gettext()
to the fallback. Otherwise, return message. Overridden in derived classes.
-
ngettext
(singular, plural, n)¶ If a fallback has been set, forward
ngettext()
to the fallback. Otherwise, return singular if n is 1; return plural otherwise. Overridden in derived classes.
-
pgettext
(context, message)¶ If a fallback has been set, forward
pgettext()
to the fallback. Otherwise, return the translated message. Overridden in derived classes.Baru pada versi 3.8.
-
npgettext
(context, singular, plural, n)¶ If a fallback has been set, forward
npgettext()
to the fallback. Otherwise, return the translated message. Overridden in derived classes.Baru pada versi 3.8.
-
lgettext
(message)¶
-
lngettext
(singular, plural, n)¶ Equivalent to
gettext()
andngettext()
, but the translation is returned as a byte string encoded in the preferred system encoding if no encoding was explicitly set withset_output_charset()
. Overridden in derived classes.Peringatan
These methods should be avoided in Python 3. See the warning for the
lgettext()
function.Deprecated since version 3.8, will be removed in version 3.10.
-
info
()¶ Return the "protected"
_info
variable, a dictionary containing the metadata found in the message catalog file.
-
charset
()¶ Return the encoding of the message catalog file.
-
output_charset
()¶ Return the encoding used to return translated messages in
lgettext()
andlngettext()
.Deprecated since version 3.8, will be removed in version 3.10.
-
set_output_charset
(charset)¶ Change the encoding used to return translated messages.
Deprecated since version 3.8, will be removed in version 3.10.
-
install
(names=None)¶ This method installs
gettext()
into the built-in namespace, binding it to_
.If the names parameter is given, it must be a sequence containing the names of functions you want to install in the builtins namespace in addition to
_()
. Supported names are'gettext'
,'ngettext'
,'pgettext'
,'npgettext'
,'lgettext'
, and'lngettext'
.Note that this is only one way, albeit the most convenient way, to make the
_()
function available to your application. Because it affects the entire application globally, and specifically the built-in namespace, localized modules should never install_()
. Instead, they should use this code to make_()
available to their module:import gettext t = gettext.translation('mymodule', ...) _ = t.gettext
This puts
_()
only in the module's global namespace and so only affects calls within this module.Berubah pada versi 3.8: Added
'pgettext'
and'npgettext'
.
-
The GNUTranslations
class¶
The gettext
module provides one additional class derived from
NullTranslations
: GNUTranslations
. This class overrides
_parse()
to enable reading GNU gettext format .mo
files
in both big-endian and little-endian format.
GNUTranslations
parses optional metadata out of the translation
catalog. It is convention with GNU gettext to include metadata as
the translation for the empty string. This metadata 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" _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, else ASCII is assumed.
Since message ids are read as Unicode strings too, all *gettext()
methods
will assume message ids as Unicode strings, not byte strings.
The entire set of key/value pairs are placed into a dictionary and set as the
"protected" _info
instance variable.
If the .mo
file's magic number is invalid, the major version number is
unexpected, or if other problems occur while reading the file, instantiating a
GNUTranslations
class can raise OSError
.
-
class
gettext.
GNUTranslations
¶ The following methods are overridden from the base class implementation:
-
gettext
(message)¶ Look up the 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 message id, and a fallback has been set, the look up is forwarded to the fallback's
gettext()
method. Otherwise, the message id is returned.
-
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 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
ngettext()
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.ngettext( 'There is %(num)d file in this directory', 'There are %(num)d files in this directory', n) % {'num': n}
-
pgettext
(context, message)¶ Look up the context and 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 message id and context, and a fallback has been set, the look up is forwarded to the fallback's
pgettext()
method. Otherwise, the message id is returned.Baru pada versi 3.8.
-
npgettext
(context, 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.
If the message id for context is not found in the catalog, and a fallback is specified, the request is forwarded to the fallback's
npgettext()
method. Otherwise, when n is 1 singular is returned, and plural is returned in all other cases.Baru pada versi 3.8.
-
lgettext
(message)¶
-
lngettext
(singular, plural, n)¶ Equivalent to
gettext()
andngettext()
, but the translation is returned as a byte string encoded in the preferred system encoding if no encoding was explicitly set withset_output_charset()
.Peringatan
These methods should be avoided in Python 3. See the warning for the
lgettext()
function.Deprecated since version 3.8, will be removed in version 3.10.
-
Solaris message catalog support¶
The Solaris operating system defines its own binary .mo
file format, but
since no documentation can be found on this format, it is not supported at this
time.
The Catalog constructor¶
GNOME uses a version of the 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 Catalog()
is an
alias for the 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
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 _()
. For example:
filename = 'mylog.txt'
message = _('writing a log message')
with open(filename, 'w') as fp:
fp.write(message)
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.
There are a few tools to extract the strings meant for translation.
The original GNU gettext only supported C or C++ source
code but its extended version xgettext scans code written
in a number of languages, including Python, to find strings marked as
translatable. Babel is a Python
internationalization library that includes a pybabel
script to
extract and compile message catalogs. François Pinard's program
called xpot does a similar job and is available as part of
his po-utils package.
(Python also includes pure-Python versions of these programs, called
pygettext.py and msgfmt.py; some Python distributions
will install them for you. pygettext.py is similar to
xgettext, but only understands Python source code and
cannot handle other programming languages such as C or C++.
pygettext.py supports a command-line interface similar to
xgettext; for details on its use, run pygettext.py
--help
. msgfmt.py is binary compatible with GNU
msgfmt. With these two programs, you may not need the GNU
gettext package to internationalize your Python
applications.)
xgettext, pygettext, and similar tools generate
.po
files that are message catalogs. They are structured
human-readable files that contain every marked string in the source
code, along with a placeholder for the translated versions of these
strings.
Copies of these .po
files are then handed over to the
individual human translators who write translations for every
supported natural language. They send back the completed
language-specific versions as a <language-name>.po
file that's
compiled into a machine-readable .mo
binary catalog file using
the msgfmt program. The .mo
files are used by the
gettext
module for the actual translation processing at
run-time.
How you use the 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 .mo
files reside in /usr/share/locale
in GNU
gettext format. Here's what you would put at the top of your
module:
import gettext
t = gettext.translation('spam', '/usr/share/locale')
_ = t.gettext
Localizing your application¶
If you are localizing your application, you can install the _()
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, you can pass it into the
install()
function:
import gettext
gettext.install('myapplication', '/usr/share/locale')
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 _()
simply returns the string
unchanged. And this dummy definition will temporarily override any definition
of _()
in the built-in namespace (until the del
command). Take
care, though if you have a previous definition of _()
in the local
namespace.
Note that the second use of _()
will not identify "a" as being
translatable to the gettext program, because the parameter
is not a string literal.
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
N_()
, which won't conflict with any definition of _()
.
However, you will need to teach your message extraction program to
look for translatable strings marked with N_()
. xgettext,
pygettext, pybabel extract
, and xpot all
support this through the use of the -k
command-line switch.
The choice of N_()
here is totally arbitrary; it could have just
as easily been MarkThisStringForTranslation()
.
Ucapan Terima Kasih¶
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
Catatan kaki
- 1
The default locale directory is system dependent; for example, on RedHat Linux it is
/usr/share/locale
, but on Solaris it is/usr/lib/locale
. Thegettext
module does not try to support these system dependent defaults; instead its default issys.base_prefix/share/locale
(seesys.base_prefix
). For this reason, it is always best to callbindtextdomain()
with an explicit absolute path at the start of your application.- 2
See the footnote for
bindtextdomain()
above.