New in version 2.1.
Warning messages are typically issued in situations where it is useful to alert the user of some condition in a program, where that condition (normally) doesn't warrant raising an exception and terminating the program. For example, one might want to issue a warning when a program uses an obsolete module.
Python programmers issue warnings by calling the warn() function defined in this module. (C programmers use PyErr_Warn(); see the Python/C API Reference Manual for details).
Warning messages are normally written to
There are two stages in warning control: first, each time a warning is issued, a determination is made whether a message should be issued or not; next, if a message is to be issued, it is formatted and printed using a user-settable hook.
The determination whether to issue a warning message is controlled by the warning filter, which is a sequence of matching rules and actions. Rules can be added to the filter by calling filterwarnings() and reset to its default state by calling resetwarnings().
The printing of warning messages is done by calling showwarning(), which may be overidden; the default implementation of this function formats the message by calling formatwarning(), which is also available for use by custom implementations.
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