22.1. `gettext` — 多语言国际化服务 ¶

源代码： 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.

22.1.1. 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 ] ) ¶

gettext. bind_textdomain_codeset ( domain [ , codeset ] ) ¶

gettext. textdomain ( [ domain ] ) ¶

gettext. gettext ( message ) ¶

gettext. lgettext ( message ) ¶

gettext. dgettext ( domain , message ) ¶

gettext. ldgettext ( domain , message ) ¶

gettext. ngettext ( singular , plural , n ) ¶

gettext. lngettext ( singular , plural , n ) ¶

gettext. dngettext ( domain , singular , plural , n ) ¶

gettext. ldngettext ( domain , singular , plural , n ) ¶

注意 GNU gettext also defines a dcgettext() method, but this was deemed not useful and so it is currently unimplemented.

这里是此 API 的典型用法范例：

import gettext
gettext.bindtextdomain('myapplication', '/path/to/my/language/directory')
gettext.textdomain('myapplication')
_ = gettext.gettext
# ...
print _('This is a translatable string.')

22.1.2. 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. Instances of this “translations” class can also install themselves in the built-in namespace as the function _() .

gettext. find ( domain [ , localedir [ , languages [ , all ] ] ] ) ¶

gettext. translation ( domain [ , localedir [ , languages [ , class_ [ , fallback [ , codeset ] ] ] ] ] ) ¶

gettext. 安装 ( domain [ , localedir [ , unicode [ , codeset [ , 名称 ] ] ] ] ) ¶

22.1.2.1. 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 ] ) ¶

_parse ( fp ) ¶

add_fallback ( fallback ) ¶

gettext ( message ) ¶

lgettext ( message ) ¶

ugettext ( message ) ¶

ngettext ( singular , plural , n ) ¶

lngettext ( singular , plural , n ) ¶

ungettext ( singular , plural , n ) ¶

info ( ) ¶

charset ( ) ¶

output_charset ( ) ¶

Return the “protected” _output_charset variable, which defines the encoding used to return translated messages.

2.4 版新增。

set_output_charset ( charset ) ¶

Change the “protected” _output_charset variable, which defines the encoding used to return translated messages.

2.4 版新增。

安装 ( [ unicode [ , 名称 ] ] ) ¶

若 unicode flag is false, this method installs self.gettext() into the built-in namespace, binding it to _ 。若 unicode is true, it binds self.ugettext() instead. By default, unicode 为 False。

若名称 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' (bound to self.gettext() or self.ugettext() 根据 unicode flag), 'ngettext' (bound to self.ngettext() or self.ungettext() 根据 unicode flag), '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.

Changed in version 2.5: 添加名称参数。

22.1.2.2. 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. It also coerces both message ids and message strings to Unicode.

GNUTranslations parses optional meta-data out of the translation catalog. It is convention with GNU gettext to include meta-data as the translation for the empty string. This meta-data 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. The ugettext() method always returns a Unicode, while the 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. ugettext() and 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” _info 实例变量。

若 .mo file’s magic number is invalid, or if other problems occur while reading the file, instantiating a GNUTranslations class can raise IOError .

The following methods are overridden from the base class implementation:

GNUTranslations. gettext ( message ) ¶: Look up the 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 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.

GNUTranslations. lgettext ( message ) ¶

相当于 gettext() , but the translation is returned in the preferred system encoding, if no other encoding was explicitly set with set_output_charset() .

2.4 版新增。

GNUTranslations. ugettext ( 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 ugettext() method. Otherwise, the message id is returned.

GNUTranslations. 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 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 ngettext() method. Otherwise, when n is 1 singular is returned, and plural is returned in all other cases.

2.3 版新增。

GNUTranslations. lngettext ( singular , plural , n ) ¶

相当于 gettext() , but the translation is returned in the preferred system encoding, if no other encoding was explicitly set with set_output_charset() .

2.4 版新增。

GNUTranslations. ungettext ( singular , plural , n ) ¶

If the message id is not found in the catalog, and a fallback is specified, the request is forwarded to the fallback’s ungettext() method. Otherwise, when n is 1 singular is returned, and plural is returned in all other cases.

这里是范例：

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}

2.3 版新增。

22.1.2.3. 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.

22.1.2.4. 分类构造函数 ¶

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.

22.1.3. 国际化您的程序和模块 ¶

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
使用 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 _() 。例如：

filename = 'mylog.txt'
message = _('writing a log message')
fp = open(filename, 'w')
fp.write(message)
fp.close()

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.

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 Tools/i18n 目录。

The pygettext 3 program scans all your Python source code looking for the strings you previously marked as translatable. It is similar to the GNU gettext program except that it understands all the intricacies of Python source code, but knows nothing about C or C++ source code. You don’t need GNU gettext unless you’re also going to be translating C code (such as C extension modules).

pygettext generates textual Uniforum-style human readable message catalog .pot files, essentially structured human readable files which contain every marked string in the source code, along with a placeholder for the translation strings. pygettext is a command line script that supports a similar command line interface as xgettext ; for details on its use, run:

pygettext.py --help

Copies of these .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 .po file. Using the msgfmt.py 4 program (in the Tools/i18n directory), you take the .po files from your translators and generate the machine-readable .mo binary catalog files. The .mo files are what the gettext module uses for the actual translation processing during 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.

22.1.3.1. 本地化您的模块 ¶

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.lgettext

If your translators were providing you with Unicode strings in their .po files, you’d instead do:

import gettext
t = gettext.translation('spam', '/usr/share/locale')
_ = t.ugettext

22.1.3.2. 本地化您的应用程序 ¶

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 or the unicode flag, you can pass these into the install() 函数：

import gettext
gettext.install('myapplication', '/usr/share/locale', unicode=1)

22.1.3.3. 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()

22.1.3.4. 延迟翻译 ¶

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 pygettext program, since it is not a string.

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_() , 5 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_() . pygettext and xpot both support this through the use of command line switches.

22.1.3.5. `gettext()` vs. `lgettext()` ¶

In Python 2.4 the 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 gettext() , which returns strings encoded with the same codeset used in the translation file, lgettext() will return strings encoded with the preferred system encoding, as returned by 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 lgettext() will return translated strings in the requested codeset, as would be expected in the GNU gettext implementation.

22.1.4. 感谢 ¶

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

脚注

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 。 gettext module does not try to support these system dependent defaults; instead its default is sys.prefix/share/locale . For this reason, it is always best to call bindtextdomain() with an explicit absolute path at the start of your application.
2: See the footnote for bindtextdomain() above.
3: François Pinard has written a program called xpot which does a similar job. It is available as part of his po-utils package .
4: msgfmt.py is binary compatible with GNU msgfmt except that it provides a simpler, all-Python implementation. With this and pygettext.py , you generally won’t need to install the GNU gettext package to internationalize your Python applications.
5: The choice of N_() here is totally arbitrary; it could have just as easily been MarkThisStringForTranslation() .

22.1. gettext — 多语言国际化服务 ¶

22.1.1. GNU gettext API ¶

22.1.2. Class-based API ¶

22.1.2.1. The NullTranslations class ¶

22.1.2.2. The GNUTranslations class ¶

22.1.2.3. Solaris message catalog support ¶

22.1.2.4. 分类构造函数 ¶

22.1.3. 国际化您的程序和模块 ¶

22.1.3.1. 本地化您的模块 ¶

22.1.3.2. 本地化您的应用程序 ¶

22.1.3.3. Changing languages on the fly ¶

22.1.3.4. 延迟翻译 ¶

22.1.3.5. gettext() vs. lgettext() ¶

22.1.4. 感谢 ¶

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22.1. `gettext` — 多语言国际化服务 ¶

22.1.2.1. The `NullTranslations` class ¶

22.1.2.2. The `GNUTranslations` class ¶

22.1.3.5. `gettext()` vs. `lgettext()` ¶