\section{\module{locale} --- Internationalization services} \declaremodule{standard}{locale} \modulesynopsis{Internationalization services.} \moduleauthor{Martin von L\"owis}{loewis@informatik.hu-berlin.de} \sectionauthor{Martin von L\"owis}{loewis@informatik.hu-berlin.de} The \module{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. The \module{locale} module is implemented on top of the \module{_locale}\refbimodindex{_locale} module, which in turn uses an ANSI C locale implementation if available. The \module{locale} module defines the following exception and functions: \begin{excdesc}{Error} Exception raised when \function{setlocale()} fails. \end{excdesc} \begin{funcdesc}{setlocale}{category\optional{, locale}} If \var{locale} is specified, it may be a string, a tuple of the form \code{(\var{language code}, \var{encoding})}, or \code{None}. If it is a tuple, it is converted to a string using the locale aliasing engine. If \var{locale} is given and not \code{None}, \function{setlocale()} modifies the locale setting for the \var{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 \exception{Error} is raised. If successful, the new locale setting is returned. If \var{locale} is omitted or \code{None}, the current setting for \var{category} is returned. \function{setlocale()} is not thread safe on most systems. Applications typically start with a call of \begin{verbatim} import locale locale.setlocale(locale.LC_ALL,"") \end{verbatim} 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[Added support for tuple values of the \var{locale} parameter]{2.0} \end{funcdesc} \begin{funcdesc}{localeconv}{} Returns the database of of the local conventions as a dictionary. This dictionary has the following strings as keys: \begin{itemize} \item \code{'decimal_point'} specifies the decimal point used in floating point number representations for the \constant{LC_NUMERIC} category. \item \code{'groupin'} is a sequence of numbers specifying at which relative positions the \code{'thousands_sep'} is expected. If the sequence is terminated with \constant{CHAR_MAX}, no further grouping is performed. If the sequence terminates with a \code{0}, the last group size is repeatedly used. \item \code{'thousands_sep'} is the character used between groups. \item \code{'int_curr_symbol'} specifies the international currency symbol from the \constant{LC_MONETARY} category. \item \code{'currency_symbol'} is the local currency symbol. \item \code{'mon_decimal_point'} is the decimal point used in monetary values. \item \code{'mon_thousands_sep'} is the separator for grouping of monetary values. \item \code{'mon_grouping'} has the same format as the \code{'grouping'} key; it is used for monetary values. \item \code{'positive_sign'} and \code{'negative_sign'} gives the sign used for positive and negative monetary quantities. \item \code{'int_frac_digits'} and \code{'frac_digits'} specify the number of fractional digits used in the international and local formatting of monetary values. \item \code{'p_cs_precedes'} and \code{'n_cs_precedes'} specifies whether the currency symbol precedes the value for positive or negative values. \item \code{'p_sep_by_space'} and \code{'n_sep_by_space'} specifies whether there is a space between the positive or negative value and the currency symbol. \item \code{'p_sign_posn'} and \code{'n_sign_posn'} indicate how the sign should be placed for positive and negative monetary values. \end{itemize} The possible values for \code{p_sign_posn} and \code{n_sign_posn} are given below. \begin{tableii}{c|l}{code}{Value}{Explanation} \lineii{0}{Currency and value are surrounded by parentheses.} \lineii{1}{The sign should precede the value and currency symbol.} \lineii{2}{The sign should follow the value and currency symbol.} \lineii{3}{The sign should immediately precede the value.} \lineii{4}{The sign should immediately follow the value.} \lineii{LC_MAX}{Nothing is specified in this locale.} \end{tableii} \end{funcdesc} \begin{funcdesc}{getdefaultlocale}{\optional{envvars}} Tries to determine the default locale settings and returns them as a tuple of the form \code{(\var{language code}, \var{encoding})}. According to \POSIX, a program which has not called \code{setlocale(LC_ALL, '')} runs using the portable \code{'C'} locale. Calling \code{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. \var{envvars} defaults to the search path used in GNU gettext; it must always contain the variable name \samp{LANG}. The GNU gettext search path contains \code{'LANGUAGE'}, \code{'LC_ALL'}, code{'LC_CTYPE'}, and \code{'LANG'}, in that order. Except for the code \code{'C'}, the language code corresponds to \rfc{1766}. \var{language code} and \var{encoding} may be \code{None} if their values cannot be determined. \versionadded{2.0} \end{funcdesc} \begin{funcdesc}{getlocale}{\optional{category}} Returns the current setting for the given locale category as tuple (language code, encoding). \var{category} may be one of the \constant{LC_*} values except \constant{LC_ALL}. It defaults to \constant{LC_CTYPE}. Except for the code \code{'C'}, the language code corresponds to \rfc{1766}. \var{language code} and \var{encoding} may be \code{None} if their values cannot be determined. \versionadded{2.0} \end{funcdesc} \begin{funcdesc}{normalize}{localename} Returns a normalized locale code for the given locale name. The returned locale code is formatted for use with \function{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 \function{setlocale()}. \versionadded{2.0} \end{funcdesc} \begin{funcdesc}{resetlocale}{\optional{category}} Sets the locale for \var{category} to the default setting. The default setting is determined by calling \function{getdefaultlocale()}. \var{category} defaults to \constant{LC_ALL}. \versionadded{2.0} \end{funcdesc} \begin{funcdesc}{strcoll}{string1, string2} Compares two strings according to the current \constant{LC_COLLATE} setting. As any other compare function, returns a negative, or a positive value, or \code{0}, depending on whether \var{string1} collates before or after \var{string2} or is equal to it. \end{funcdesc} \begin{funcdesc}{strxfrm}{string} Transforms a string to one that can be used for the built-in function \function{cmp()}\bifuncindex{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. \end{funcdesc} \begin{funcdesc}{format}{format, val\optional{, grouping}} Formats a number \var{val} according to the current \constant{LC_NUMERIC} setting. The format follows the conventions of the \code{\%} operator. For floating point values, the decimal point is modified if appropriate. If \var{grouping} is true, also takes the grouping into account. \end{funcdesc} \begin{funcdesc}{str}{float} Formats a floating point number using the same format as the built-in function \code{str(\var{float})}, but takes the decimal point into account. \end{funcdesc} \begin{funcdesc}{atof}{string} Converts a string to a floating point number, following the \constant{LC_NUMERIC} settings. \end{funcdesc} \begin{funcdesc}{atoi}{string} Converts a string to an integer, following the \constant{LC_NUMERIC} conventions. \end{funcdesc} \begin{datadesc}{LC_CTYPE} \refstmodindex{string} Locale category for the character type functions. Depending on the settings of this category, the functions of module \refmodule{string} dealing with case change their behaviour. \end{datadesc} \begin{datadesc}{LC_COLLATE} Locale category for sorting strings. The functions \function{strcoll()} and \function{strxfrm()} of the \module{locale} module are affected. \end{datadesc} \begin{datadesc}{LC_TIME} Locale category for the formatting of time. The function \function{time.strftime()} follows these conventions. \end{datadesc} \begin{datadesc}{LC_MONETARY} Locale category for formatting of monetary values. The available options are available from the \function{localeconv()} function. \end{datadesc} \begin{datadesc}{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 \function{os.strerror()} might be affected by this category. \end{datadesc} \begin{datadesc}{LC_NUMERIC} Locale category for formatting numbers. The functions \function{format()}, \function{atoi()}, \function{atof()} and \function{str()} of the \module{locale} module are affected by that category. All other numeric formatting operations are not affected. \end{datadesc} \begin{datadesc}{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. \end{datadesc} \begin{datadesc}{CHAR_MAX} This is a symbolic constant used for different values returned by \function{localeconv()}. \end{datadesc} Example: \begin{verbatim} >>> import locale >>> loc = locale.setlocale(locale.LC_ALL) # get current locale >>> locale.setlocale(locale.LC_ALL, "de") # use German locale >>> locale.strcoll("f\344n", "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 \end{verbatim} \subsection{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 \samp{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 \code{setlocale(LC_ALL, "")}. It is generally a bad idea to call \function{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 (e.g. \function{string.lower()}, or certain formats used with \function{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-\samp{C} locale settings. The case conversion functions in the \refmodule{string}\refstmodindex{string} and \module{strop}\refbimodindex{strop} modules are affected by the locale settings. When a call to the \function{setlocale()} function changes the \constant{LC_CTYPE} settings, the variables \code{string.lowercase}, \code{string.uppercase} and \code{string.letters} (and their counterparts in \module{strop}) are recalculated. Note that this code that uses these variable through `\keyword{from} ... \keyword{import} ...', e.g. \code{from string import letters}, is not affected by subsequent \function{setlocale()} calls. The only way to perform numeric operations according to the locale is to use the special functions defined by this module: \function{atof()}, \function{atoi()}, \function{format()}, \function{str()}. \subsection{For extension writers and programs that embed Python \label{embedding-locale}} Extension modules should never call \function{setlocale()}, except to find out what the current locale is. But since the return value can only be used portably to restore it, that is not very useful (except perhaps to find out whether or not the locale is \samp{C}). When Python is embedded in an application, if the application sets the locale to something specific before initializing Python, that is generally okay, and Python will use whatever locale is set, \emph{except} that the \constant{LC_NUMERIC} locale should always be \samp{C}. The \function{setlocale()} function in the \module{locale} module gives the Python programmer the impression that you can manipulate the \constant{LC_NUMERIC} locale setting, but this not the case at the C level: C code will always find that the \constant{LC_NUMERIC} locale setting is \samp{C}. This is because too much would break when the decimal point character is set to something else than a period (e.g. the Python parser would break). Caveat: threads that run without holding Python's global interpreter lock may occasionally find that the numeric locale setting differs; this is because the only portable way to implement this feature is to set the numeric locale settings to what the user requests, extract the relevant characteristics, and then restore the \samp{C} numeric locale. When Python code uses the \module{locale} module to change the locale, this also affects the embedding application. If the embedding application doesn't want this to happen, it should remove the \module{_locale} extension module (which does all the work) from the table of built-in modules in the \file{config.c} file, and make sure that the \module{_locale} module is not accessible as a shared library.