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| 55 | <H2><A NAME="SECTION0082710000000000000000"> |
| 56 | 6.27.1 Background, details, hints, tips and caveats</A> |
| 57 | </H2> |
| 58 | |
| 59 | <P> |
| 60 | The C standard defines the locale as a program-wide property that may |
| 61 | be relatively expensive to change. On top of that, some |
| 62 | implementation are broken in such a way that frequent locale changes |
| 63 | may cause core dumps. This makes the locale somewhat painful to use |
| 64 | correctly. |
| 65 | |
| 66 | <P> |
| 67 | Initially, when a program is started, the locale is the "<tt class="samp">C</tt>" locale, no |
| 68 | matter what the user's preferred locale is. The program must |
| 69 | explicitly say that it wants the user's preferred locale settings by |
| 70 | calling <code>setlocale(LC_ALL, '')</code>. |
| 71 | |
| 72 | <P> |
| 73 | It is generally a bad idea to call <tt class="function">setlocale()</tt> in some library |
| 74 | routine, since as a side effect it affects the entire program. Saving |
| 75 | and restoring it is almost as bad: it is expensive and affects other |
| 76 | threads that happen to run before the settings have been restored. |
| 77 | |
| 78 | <P> |
| 79 | If, when coding a module for general use, you need a locale |
| 80 | independent version of an operation that is affected by the locale |
| 81 | (such as <tt class="function">string.lower()</tt>, or certain formats used with |
| 82 | <tt class="function">time.strftime()</tt>), you will have to find a way to do it |
| 83 | without using the standard library routine. Even better is convincing |
| 84 | yourself that using locale settings is okay. Only as a last resort |
| 85 | should you document that your module is not compatible with |
| 86 | non-"<tt class="samp">C</tt>" locale settings. |
| 87 | |
| 88 | <P> |
| 89 | The case conversion functions in the |
| 90 | <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 |
| 91 | locale settings. When a call to the <tt class="function">setlocale()</tt> function |
| 92 | changes the <tt class="constant">LC_CTYPE</tt> settings, the variables |
| 93 | <code>string.lowercase</code>, <code>string.uppercase</code> and |
| 94 | <code>string.letters</code> are recalculated. Note that this code that uses |
| 95 | these variable through `<tt class="keyword">from</tt> ... <tt class="keyword">import</tt> ...', |
| 96 | e.g. <code>from string import letters</code>, is not affected by subsequent |
| 97 | <tt class="function">setlocale()</tt> calls. |
| 98 | |
| 99 | <P> |
| 100 | The only way to perform numeric operations according to the locale |
| 101 | is to use the special functions defined by this module: |
| 102 | <tt class="function">atof()</tt>, <tt class="function">atoi()</tt>, <tt class="function">format()</tt>, |
| 103 | <tt class="function">str()</tt>. |
| 104 | |
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| 141 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> |
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