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<H2><A NAME="SECTION0052030000000000000000"></A><A NAME="warning-functions"></A>
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3.20.3 Available Functions
</H2>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-689' xml:id='l2h-689' class="function">warn</tt></b>(</nobr></td>
  <td><var>message</var><big>[</big><var>, category</var><big>[</big><var>, stacklevel</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Issue a warning, or maybe ignore it or raise an exception.  The
<var>category</var> argument, if given, must be a warning category class
(see above); it defaults to <tt class="exception">UserWarning</tt>.  Alternatively
<var>message</var> can be a <tt class="exception">Warning</tt> instance, in which case
<var>category</var> will be ignored and <code>message.__class__</code> will be used.
In this case the message text will be <code>str(message)</code>. This function
raises an exception if the particular warning issued is changed
into an error by the warnings filter see above.  The <var>stacklevel</var>
argument can be used by wrapper functions written in Python, like
this:

<P>
<div class="verbatim"><pre>
def deprecation(message):
    warnings.warn(message, DeprecationWarning, stacklevel=2)
</pre></div>

<P>
This makes the warning refer to <tt class="function">deprecation()</tt>'s caller,
rather than to the source of <tt class="function">deprecation()</tt> itself (since
the latter would defeat the purpose of the warning message).
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-690' xml:id='l2h-690' class="function">warn_explicit</tt></b>(</nobr></td>
  <td><var>message, category, filename,
 lineno</var><big>[</big><var>, module</var><big>[</big><var>, registry</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
This is a low-level interface to the functionality of
<tt class="function">warn()</tt>, passing in explicitly the message, category,
filename and line number, and optionally the module name and the
registry (which should be the <code>__warningregistry__</code> dictionary of
the module).  The module name defaults to the filename with <code>.py</code>
stripped; if no registry is passed, the warning is never suppressed.
<var>message</var> must be a string and <var>category</var> a subclass of
<tt class="exception">Warning</tt> or <var>message</var> may be a <tt class="exception">Warning</tt> instance,
in which case <var>category</var> will be ignored.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-691' xml:id='l2h-691' class="function">showwarning</tt></b>(</nobr></td>
  <td><var>message, category, filename,
                             lineno</var><big>[</big><var>, file</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Write a warning to a file.  The default implementation calls
<code>formatwarning(<var>message</var>, <var>category</var>, <var>filename</var>,
<var>lineno</var>)</code> and writes the resulting string to <var>file</var>, which
defaults to <code>sys.stderr</code>.  You may replace this function with an
alternative implementation by assigning to
<code>warnings.showwarning</code>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-692' xml:id='l2h-692' class="function">formatwarning</tt></b>(</nobr></td>
  <td><var>message, category, filename, lineno</var>)</td></tr></table></dt>
<dd>
Format a warning the standard way.  This returns a string  which may
contain embedded newlines and ends in a newline.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-693' xml:id='l2h-693' class="function">filterwarnings</tt></b>(</nobr></td>
  <td><var>action</var><big>[</big><var>,
                 message</var><big>[</big><var>, category</var><big>[</big><var>,
                 module</var><big>[</big><var>, lineno</var><big>[</big><var>, append</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Insert an entry into the list of warnings filters.  The entry is
inserted at the front by default; if <var>append</var> is true, it is
inserted at the end.
This checks the types of the arguments, compiles the message and
module regular expressions, and inserts them as a tuple in front
of the warnings filter.  Entries inserted later override entries
inserted earlier, if both match a particular warning.  Omitted
arguments default to a value that matches everything.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-694' xml:id='l2h-694' class="function">resetwarnings</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Reset the warnings filter.  This discards the effect of all previous
calls to <tt class="function">filterwarnings()</tt>, including that of the
<b class="programopt">-W</b> command line options.
</dl>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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