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(python2.1-lib.info)Background

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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 `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.
`string.lower()', or certain formats used with `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.

The case conversion functions in the `string'  module are affected by
the locale settings.  When a call to the `setlocale()' function changes
the `LC_CTYPE' settings, the variables `string.lowercase',
`string.uppercase' and `string.letters' are recalculated.  Note that
this code that uses these variable through ``from' ... `import' ...',
e.g. `from string import letters', is not affected by subsequent
`setlocale()' calls.

The only way to perform numeric operations according to the locale is
to use the special functions defined by this module: `atof()',
`atoi()', `format()', `str()'.