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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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