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  $   	€l–Эm_JJhҐ І ёИ®41hЯГ„ој/ВБА ?ч     	:mod:`warnings` --- Warning control
===================================

.. index:: single: warnings

.. module:: warnings
   :synopsis: Issue warning messages and control their disposition.


.. versionadded:: 2.1

**Source code:** :source:`Lib/warnings.py`

--------------

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 :func:`warn` function defined
in this module.  (C programmers use :c:func:`PyErr_WarnEx`; see
:ref:`exceptionhandling` for details).

Warning messages are normally written to ``sys.stderr``, but their disposition
can be changed flexibly, from ignoring all warnings to turning them into
exceptions.  The disposition of warnings can vary based on the warning category
(see below), the text of the warning message, and the source location where it
is issued.  Repetitions of a particular warning for the same source location are
typically suppressed.

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 :func:`filterwarnings` and reset to its default
state by calling :func:`resetwarnings`.

The printing of warning messages is done by calling :func:`showwarning`, which
may be overridden; the default implementation of this function formats the
message by calling :func:`formatwarning`, which is also available for use by
custom implementations.

.. seealso::
   :func:`logging.captureWarnings` allows you to handle all warnings with
   the standard logging infrastructure.


.. _warning-categories:

Warning Categories
------------------

There are a number of built-in exceptions that represent warning categories.
This categorization is useful to be able to filter out groups of warnings.  The
following warnings category classes are currently defined:

.. tabularcolumns:: |l|p{0.6\linewidth}|

+----------------------------------+-----------------------------------------------+
| Class                            | Description                                   |
+==================================+===============================================+
| :exc:`Warning`                   | This is the base class of all warning         |
|                                  | category classes.  It is a subclass of        |
|                                  | :exc:`Exception`.                             |
+----------------------------------+-----------------------------------------------+
| :exc:`UserWarning`               | The default category for :func:`warn`.        |
+----------------------------------+-----------------------------------------------+
| :exc:`DeprecationWarning`        | Base category for warnings about deprecated   |
|                                  | features (ignored by default).                |
+----------------------------------+-----------------------------------------------+
| :exc:`SyntaxWarning`             | Base category for warnings about dubious      |
|                                  | syntactic features.                           |
+----------------------------------+-----------------------------------------------+
| :exc:`RuntimeWarning`            | Base category for warnings about dubious      |
|                                  | runtime features.                             |
+----------------------------------+-----------------------------------------------+
| :exc:`