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54 | ||
55 | <H1><A NAME="SECTION0052000000000000000000"> | |
56 | 3.20 <tt class="module">warnings</tt> -- | |
57 | Warning control</A> | |
58 | </H1> | |
59 | ||
60 | <P> | |
61 | <A NAME="module-warnings"></A> | |
62 | <a id='l2h-688' xml:id='l2h-688'></a> | |
63 | ||
64 | <P> | |
65 | ||
66 | <span class="versionnote">New in version 2.1.</span> | |
67 | ||
68 | <P> | |
69 | Warning messages are typically issued in situations where it is useful | |
70 | to alert the user of some condition in a program, where that condition | |
71 | (normally) doesn't warrant raising an exception and terminating the | |
72 | program. For example, one might want to issue a warning when a | |
73 | program uses an obsolete module. | |
74 | ||
75 | <P> | |
76 | Python programmers issue warnings by calling the <tt class="function">warn()</tt> | |
77 | function defined in this module. (C programmers use | |
78 | <tt class="cfunction">PyErr_Warn()</tt>; see the | |
79 | <em class="citetitle"><a | |
80 | href="../api/exceptionHandling.html" | |
81 | title="Python/C API Reference | |
82 | Manual" | |
83 | >Python/C API Reference | |
84 | Manual</a></em> for details). | |
85 | ||
86 | <P> | |
87 | Warning messages are normally written to <code>sys.stderr</code>, but their | |
88 | disposition can be changed flexibly, from ignoring all warnings to | |
89 | turning them into exceptions. The disposition of warnings can vary | |
90 | based on the warning category (see below), the text of the warning | |
91 | message, and the source location where it is issued. Repetitions of a | |
92 | particular warning for the same source location are typically | |
93 | suppressed. | |
94 | ||
95 | <P> | |
96 | There are two stages in warning control: first, each time a warning is | |
97 | issued, a determination is made whether a message should be issued or | |
98 | not; next, if a message is to be issued, it is formatted and printed | |
99 | using a user-settable hook. | |
100 | ||
101 | <P> | |
102 | The determination whether to issue a warning message is controlled by | |
103 | the warning filter, which is a sequence of matching rules and actions. | |
104 | Rules can be added to the filter by calling | |
105 | <tt class="function">filterwarnings()</tt> and reset to its default state by calling | |
106 | <tt class="function">resetwarnings()</tt>. | |
107 | ||
108 | <P> | |
109 | The printing of warning messages is done by calling | |
110 | <tt class="function">showwarning()</tt>, which may be overridden; the default | |
111 | implementation of this function formats the message by calling | |
112 | <tt class="function">formatwarning()</tt>, which is also available for use by custom | |
113 | implementations. | |
114 | ||
115 | <P> | |
116 | ||
117 | <p><br /></p><hr class='online-navigation' /> | |
118 | <div class='online-navigation'> | |
119 | <!--Table of Child-Links--> | |
120 | <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a> | |
121 | ||
122 | <UL CLASS="ChildLinks"> | |
123 | <LI><A href="warning-categories.html">3.20.1 Warning Categories</a> | |
124 | <LI><A href="warning-filter.html">3.20.2 The Warnings Filter</a> | |
125 | <LI><A href="warning-functions.html">3.20.3 Available Functions</a> | |
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164 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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