:mod:`locale` --- Internationalization services

===============================================

.. module:: locale

   :synopsis: Internationalization services.

.. moduleauthor:: Martin von Löwis <martin@v.loewis.de>

.. sectionauthor:: Martin von Löwis <martin@v.loewis.de>

The :mod:`locale` module opens access to the POSIX locale database and

functionality. The POSIX locale mechanism allows programmers to deal with

certain cultural issues in an application, without requiring the programmer to

know all the specifics of each country where the software is executed.

.. index:: module: _locale

The :mod:`locale` module is implemented on top of the :mod:`_locale` module,

which in turn uses an ANSI C locale implementation if available.

The :mod:`locale` module defines the following exception and functions:

.. exception:: Error

   Exception raised when :func:`setlocale` fails.

.. function:: setlocale(category[, locale])

   If *locale* is specified, it may be a string, a tuple of the form ``(language

   code, encoding)``, or ``None``. If it is a tuple, it is converted to a string

   using the locale aliasing engine.  If *locale* is given and not ``None``,

   :func:`setlocale` modifies the locale setting for the *category*.  The available

   categories are listed in the data description below.  The value is the name of a

   locale.  An empty string specifies the user's default settings. If the

   modification of the locale fails, the exception :exc:`Error` is raised.  If

   successful, the new locale setting is returned.

   If *locale* is omitted or ``None``, the current setting for *category* is

   returned.

   :func:`setlocale` is not thread safe on most systems. Applications typically

   start with a call of ::

      import locale

      locale.setlocale(locale.LC_ALL, '')

   This sets the locale for all categories to the user's default setting (typically

   specified in the :envvar:`LANG` environment variable).  If the locale is not

   changed thereafter, using multithreading should not cause problems.

   .. versionchanged:: 2.0

      Added support for tuple values of the *locale* parameter.

.. function:: localeconv()

   Returns the database of the local conventions as a dictionary. This dictionary

   has the following strings as keys:

   +----------------------+-------------------------------------+--------------------------------+

   | Category             | Key                                 | Meaning                        |

   +======================+=====================================+================================+

   | :const:`LC_NUMERIC`  | ``'decimal_point'``                 | Decimal point character.       |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'grouping'``                      | Sequence of numbers specifying |

   |                      |                                     | which relative positions the   |

   |                      |                                     | ``'thousands_sep'`` is         |

   |                      |                                     | expected.  If the sequence is  |

   |                      |                                     | terminated with                |

   |                      |                                     | :const:`CHAR_MAX`, no further  |

   |                      |                                     | grouping is performed. If the  |

   |                      |                                     | sequence terminates with a     |

   |                      |                                     | ``0``,  the last group size is |

   |                      |                                     | repeatedly used.               |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'thousands_sep'``                 | Character used between groups. |

   +----------------------+-------------------------------------+--------------------------------+

   | :const:`LC_MONETARY` | ``'int_curr_symbol'``               | International currency symbol. |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'currency_symbol'``               | Local currency symbol.         |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'p_cs_precedes/n_cs_precedes'``   | Whether the currency symbol    |

   |                      |                                     | precedes the value (for        |

   |                      |                                     | positive resp. negative        |

   |                      |                                     | values).                       |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'p_sep_by_space/n_sep_by_space'`` | Whether the currency symbol is |

   |                      |                                     | separated from the value  by a |

   |                      |                                     | space (for positive resp.      |

   |                      |                                     | negative values).              |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'mon_decimal_point'``             | Decimal point used for         |

   |                      |                                     | monetary values.               |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'frac_digits'``                   | Number of fractional digits    |

   |                      |                                     | used in local formatting of    |

   |                      |                                     | monetary values.               |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'int_frac_digits'``               | Number of fractional digits    |

   |                      |                                     | used in international          |

   |                      |                                     | formatting of monetary values. |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'mon_thousands_sep'``             | Group separator used for       |

   |                      |                                     | monetary values.               |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'mon_grouping'``                  | Equivalent to ``'grouping'``,  |

   |                      |                                     | used for monetary values.      |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'positive_sign'``                 | Symbol used to annotate a      |

   |                      |                                     | positive monetary value.       |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'negative_sign'``                 | Symbol used to annotate a      |

   |                      |                                     | negative monetary value.       |

   +----------------------+-------------------------------------+--------------------------------+

   |                      | ``'p_sign_posn/n_sign_posn'``       | The position of the sign (for  |

   |                      |                                     | positive resp. negative        |

   |                      |                                     | values), see below.            |

   +----------------------+-------------------------------------+--------------------------------+

   All numeric values can be set to :const:`CHAR_MAX` to indicate that there is no

   value specified in this locale.

   The possible values for ``'p_sign_posn'`` and ``'n_sign_posn'`` are given below.

   +--------------+-----------------------------------------+

   | Value        | Explanation                             |

   +==============+=========================================+

   | ``0``        | Currency and value are surrounded by    |

   |              | parentheses.                            |

   +--------------+-----------------------------------------+

   | ``1``        | The sign should precede the value and   |

   |              | currency symbol.                        |

   +--------------+-----------------------------------------+

   | ``2``        | The sign should follow the value and    |

   |              | currency symbol.                        |

   +--------------+-----------------------------------------+

   | ``3``        | The sign should immediately precede the |

   |              | value.                                  |

   +--------------+-----------------------------------------+

   | ``4``        | The sign should immediately follow the  |

   |              | value.                                  |

   +--------------+-----------------------------------------+

   | ``CHAR_MAX`` | Nothing is specified in this locale.    |

   +--------------+-----------------------------------------+

.. function:: nl_langinfo(option)

   Return some locale-specific information as a string. This function is not

   available on all systems, and the set of possible options might also vary across

   platforms. The possible argument values are numbers, for which symbolic

   constants are available in the locale module.

.. function:: getdefaultlocale([envvars])

   Tries to determine the default locale settings and returns them as a tuple of

   the form ``(language code, encoding)``.

   According to POSIX, a program which has not called ``setlocale(LC_ALL, '')``

   runs using the portable ``'C'`` locale.  Calling ``setlocale(LC_ALL, '')`` lets

   it use the default locale as defined by the :envvar:`LANG` variable.  Since we

   do not want to interfere with the current locale setting we thus emulate the

   behavior in the way described above.

   To maintain compatibility with other platforms, not only the :envvar:`LANG`

   variable is tested, but a list of variables given as envvars parameter.  The

   first found to be defined will be used.  *envvars* defaults to the search path

   used in GNU gettext; it must always contain the variable name ``LANG``.  The GNU

   gettext search path contains ``'LANGUAGE'``, ``'LC_ALL'``, ``'LC_CTYPE'``, and

   ``'LANG'``, in that order.

   Except for the code ``'C'``, the language code corresponds to :rfc:`1766`.

   *language code* and *encoding* may be ``None`` if their values cannot be

   determined.

   .. versionadded:: 2.0

.. function:: getlocale([category])

   Returns the current setting for the given locale category as sequence containing

   *language code*, *encoding*. *category* may be one of the :const:`LC_\*` values

   except :const:`LC_ALL`.  It defaults to :const:`LC_CTYPE`.

   Except for the code ``'C'``, the language code corresponds to :rfc:`1766`.

   *language code* and *encoding* may be ``None`` if their values cannot be

   determined.

   .. versionadded:: 2.0

.. function:: getpreferredencoding([do_setlocale])

   Return the encoding used for text data, according to user preferences.  User

   preferences are expressed differently on different systems, and might not be

   available programmatically on some systems, so this function only returns a

   guess.

   On some systems, it is necessary to invoke :func:`setlocale` to obtain the user

   preferences, so this function is not thread-safe. If invoking setlocale is not

   necessary or desired, *do_setlocale* should be set to ``False``.

   .. versionadded:: 2.3

.. function:: normalize(localename)

   Returns a normalized locale code for the given locale name.  The returned locale

   code is formatted for use with :func:`setlocale`.  If normalization fails, the

   original name is returned unchanged.

   If the given encoding is not known, the function defaults to the default

   encoding for the locale code just like :func:`setlocale`.

   .. versionadded:: 2.0

.. function:: resetlocale([category])

   Sets the locale for *category* to the default setting.

   The default setting is determined by calling :func:`getdefaultlocale`.

   *category* defaults to :const:`LC_ALL`.

   .. versionadded:: 2.0

.. function:: strcoll(string1, string2)

   Compares two strings according to the current :const:`LC_COLLATE` setting. As

   any other compare function, returns a negative, or a positive value, or ``0``,

   depending on whether *string1* collates before or after *string2* or is equal to

   it.

.. function:: strxfrm(string)

   .. index:: builtin: cmp

   Transforms a string to one that can be used for the built-in function

   :func:`cmp`, and still returns locale-aware results.  This function can be used

   when the same string is compared repeatedly, e.g. when collating a sequence of

   strings.

.. function:: format(format, val[, grouping[, monetary]])

   Formats a number *val* according to the current :const:`LC_NUMERIC` setting.

   The format follows the conventions of the ``%`` operator.  For floating point

   values, the decimal point is modified if appropriate.  If *grouping* is true,

   also takes the grouping into account.

   If *monetary* is true, the conversion uses monetary thousands separator and

   grouping strings.

   Please note that this function will only work for exactly one %char specifier.

   For whole format strings, use :func:`format_string`.

   .. versionchanged:: 2.5

      Added the *monetary* parameter.

.. function:: format_string(format, val[, grouping])

   Processes formatting specifiers as in ``format % val``, but takes the current

   locale settings into account.

   .. versionadded:: 2.5

.. function:: currency(val[, symbol[, grouping[, international]]])

   Formats a number *val* according to the current :const:`LC_MONETARY` settings.

   The returned string includes the currency symbol if *symbol* is true, which is

   the default. If *grouping* is true (which is not the default), grouping is done

   with the value. If *international* is true (which is not the default), the

   international currency symbol is used.

   Note that this function will not work with the 'C' locale, so you have to set a

   locale via :func:`setlocale` first.

   .. versionadded:: 2.5

.. function:: str(float)

   Formats a floating point number using the same format as the built-in function

   ``str(float)``, but takes the decimal point into account.

.. function:: atof(string)

   Converts a string to a floating point number, following the :const:`LC_NUMERIC`

   settings.

.. function:: atoi(string)

   Converts a string to an integer, following the :const:`LC_NUMERIC` conventions.

.. data:: LC_CTYPE

   .. index:: module: string

   Locale category for the character type functions.  Depending on the settings of

   this category, the functions of module :mod:`string` dealing with case change

   their behaviour.

.. data:: LC_COLLATE

   Locale category for sorting strings.  The functions :func:`strcoll` and

   :func:`strxfrm` of the :mod:`locale` module are affected.

.. data:: LC_TIME

   Locale category for the formatting of time.  The function :func:`time.strftime`

   follows these conventions.

.. data:: LC_MONETARY

   Locale category for formatting of monetary values.  The available options are

   available from the :func:`localeconv` function.

.. data:: LC_MESSAGES

   Locale category for message display. Python currently does not support

   application specific locale-aware messages.  Messages displayed by the operating

   system, like those returned by :func:`os.strerror` might be affected by this

   category.

.. data:: LC_NUMERIC

   Locale category for formatting numbers.  The functions :func:`format`,

   :func:`atoi`, :func:`atof` and :func:`str` of the :mod:`locale` module are

   affected by that category.  All other numeric formatting operations are not

   affected.

.. data:: LC_ALL

   Combination of all locale settings.  If this flag is used when the locale is

   changed, setting the locale for all categories is attempted. If that fails for

   any category, no category is changed at all.  When the locale is retrieved using

   this flag, a string indicating the setting for all categories is returned. This

   string can be later used to restore the settings.

.. data:: CHAR_MAX

   This is a symbolic constant used for different values returned by

   :func:`localeconv`.

The :func:`nl_langinfo` function accepts one of the following keys. Most

descriptions are taken from the corresponding description in the GNU C library.

.. data:: CODESET

   Return a string with the name of the character encoding used in the selected

   locale.

.. data:: D_T_FMT

   Return a string that can be used as a format string for strftime(3) to represent

   time and date in a locale-specific way.

.. data:: D_FMT

   Return a string that can be used as a format string for strftime(3) to represent

   a date in a locale-specific way.

.. data:: T_FMT

   Return a string that can be used as a format string for strftime(3) to represent

   a time in a locale-specific way.

.. data:: T_FMT_AMPM

   The return value can be used as a format string for 'strftime' to represent time

   in the am/pm format.

.. data:: DAY_1 ... DAY_7

   Return name of the n-th day of the week.

   .. warning::

      This follows the US convention of :const:`DAY_1` being Sunday, not the

      international convention (ISO 8601) that Monday is the first day of the week.

.. data:: ABDAY_1 ... ABDAY_7

   Return abbreviated name of the n-th day of the week.

.. data:: MON_1 ... MON_12

   Return name of the n-th month.

.. data:: ABMON_1 ... ABMON_12

   Return abbreviated name of the n-th month.

.. data:: RADIXCHAR

   Return radix character (decimal dot, decimal comma, etc.)

.. data:: THOUSEP

   Return separator character for thousands (groups of three digits).

.. data:: YESEXPR

   Return a regular expression that can be used with the regex function to

   recognize a positive response to a yes/no question.

   .. warning::

      The expression is in the syntax suitable for the :cfunc:`regex` function from

      the C library, which might differ from the syntax used in :mod:`re`.

.. data:: NOEXPR

   Return a regular expression that can be used with the regex(3) function to

   recognize a negative response to a yes/no question.

.. data:: CRNCYSTR

   Return the currency symbol, preceded by "-" if the symbol should appear before

   the value, "+" if the symbol should appear after the value, or "." if the symbol

   should replace the radix character.

.. data:: ERA

   The return value represents the era used in the current locale.

   Most locales do not define this value.  An example of a locale which does define

   this value is the Japanese one.  In Japan, the traditional representation of

   dates includes the name of the era corresponding to the then-emperor's reign.

   Normally it should not be necessary to use this value directly. Specifying the

   ``E`` modifier in their format strings causes the :func:`strftime` function to

   use this information.  The format of the returned string is not specified, and

   therefore you should not assume knowledge of it on different systems.

.. data:: ERA_YEAR

   The return value gives the year in the relevant era of the locale.

.. data:: ERA_D_T_FMT

   This return value can be used as a format string for :func:`strftime` to

   represent dates and times in a locale-specific era-based way.

.. data:: ERA_D_FMT

   This return value can be used as a format string for :func:`strftime` to

   represent time in a locale-specific era-based way.

.. data:: ALT_DIGITS

   The return value is a representation of up to 100 values used to represent the

   values 0 to 99.

Example::

   >>> import locale

   >>> loc = locale.getlocale(locale.LC_ALL) # get current locale

   >>> locale.setlocale(locale.LC_ALL, 'de_DE') # use German locale; name might vary with platform

   >>> locale.strcoll('f\xe4n', 'foo') # compare a string containing an umlaut 

   >>> locale.setlocale(locale.LC_ALL, '') # use user's preferred locale

   >>> locale.setlocale(locale.LC_ALL, 'C') # use default (C) locale

   >>> locale.setlocale(locale.LC_ALL, loc) # restore saved locale

Background, details, hints, tips and caveats

--------------------------------------------

The C standard defines the locale as a program-wide property that may be

relatively expensive to change.  On top of that, some implementation are broken

in such a way that frequent locale changes may cause core dumps.  This makes the

locale somewhat painful to use correctly.

Initially, when a program is started, the locale is the ``C`` locale, no matter

what the user's preferred locale is.  The program must explicitly say that it

wants the user's preferred locale settings by calling ``setlocale(LC_ALL, '')``.

It is generally a bad idea to call :func:`setlocale` in some library routine,

since as a side effect it affects the entire program.  Saving and restoring it

is almost as bad: it is expensive and affects other threads that happen to run

before the settings have been restored.

If, when coding a module for general use, you need a locale independent version

of an operation that is affected by the locale (such as :func:`string.lower`, or

certain formats used with :func:`time.strftime`), you will have to find a way to

do it without using the standard library routine.  Even better is convincing

yourself that using locale settings is okay.  Only as a last resort should you

document that your module is not compatible with non-\ ``C`` locale settings.

.. index:: module: string