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<title>6.27.1 Background, details, hints, tips and caveats
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<H2><A NAME=
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6.27.1 Background, details, hints, tips and caveats
</A>
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
Initially, when a program is started, the locale is the
"<tt class="samp
">C</tt>" 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, '')
</code>.
It is generally a bad idea to call
<tt class=
"function">setlocale()
</tt> 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
<tt class=
"function">string.lower()
</tt>, or certain formats used with
<tt class=
"function">time.strftime()
</tt>), 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-
"<tt class="samp
">C</tt>" locale settings.
The case conversion functions in the
<tt class=
"module"><a href=
"module-string.html">string
</a></tt><a id='l2h-
2410' xml:id='l2h-
2410'
></a> module are affected by the
locale settings. When a call to the
<tt class=
"function">setlocale()
</tt> function
changes the
<tt class=
"constant">LC_CTYPE
</tt> settings, the variables
<code>string.lowercase
</code>,
<code>string.uppercase
</code> and
<code>string.letters
</code> are recalculated. Note that this code that uses
these variable through `
<tt class=
"keyword">from
</tt> ...
<tt class=
"keyword">import
</tt> ...',
e.g.
<code>from string import letters
</code>, is not affected by subsequent
<tt class=
"function">setlocale()
</tt> calls.
The only way to perform numeric operations according to the locale
is to use the special functions defined by this module:
<tt class=
"function">atof()
</tt>,
<tt class=
"function">atoi()
</tt>,
<tt class=
"function">format()
</tt>,
<tt class=
"function">str()
</tt>.
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<span class=
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2.4.2, documentation updated on
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2005.
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