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<div class="section" id="module-exceptions">
<span id="bltin-exceptions"></span><h1>6. Built-in Exceptions<a class="headerlink" href="#module-exceptions" title="Permalink to this headline">¶</a></h1>
<p>Exceptions should be class objects. The exceptions are defined in the module
<tt class="xref docutils literal"><span class="pre">exceptions</span></tt>. This module never needs to be imported explicitly: the
exceptions are provided in the built-in namespace as well as the
<tt class="xref docutils literal"><span class="pre">exceptions</span></tt> module.</p>
<p id="index-329">For class exceptions, in a <a class="reference external" href="../reference/compound_stmts.html#try"><tt class="xref docutils literal"><span class="pre">try</span></tt></a> statement with an <a class="reference external" href="../reference/compound_stmts.html#except"><tt class="xref docutils literal"><span class="pre">except</span></tt></a>
clause that mentions a particular class, that clause also handles any exception
classes derived from that class (but not exception classes from which <em>it</em> is
derived). Two exception classes that are not related via subclassing are never
equivalent, even if they have the same name.</p>
<p id="index-330">The built-in exceptions listed below can be generated by the interpreter or
built-in functions. Except where mentioned, they have an “associated value”
indicating the detailed cause of the error. This may be a string or a tuple
containing several items of information (e.g., an error code and a string
explaining the code). The associated value is the second argument to the
<a class="reference external" href="../reference/simple_stmts.html#raise"><tt class="xref docutils literal"><span class="pre">raise</span></tt></a> statement. If the exception class is derived from the standard
root class <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a>, the associated value is present as the
exception instance’s <tt class="xref docutils literal"><span class="pre">args</span></tt> attribute.</p>
<p>User code can raise built-in exceptions. This can be used to test an exception
handler or to report an error condition “just like” the situation in which the
interpreter raises the same exception; but beware that there is nothing to
prevent user code from raising an inappropriate error.</p>
<p>The built-in exception classes can be sub-classed to define new exceptions;
programmers are encouraged to at least derive new exceptions from the
<a title="exceptions.Exception" class="reference internal" href="#exceptions.Exception"><tt class="xref docutils literal"><span class="pre">Exception</span></tt></a> class and not <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a>. More information on
defining exceptions is available in the Python Tutorial under
<a class="reference external" href="../tutorial/errors.html#tut-userexceptions"><em>User-defined Exceptions</em></a>.</p>
<p>The following exceptions are only used as base classes for other exceptions.</p>
<dl class="exception">
<dt id="exceptions.BaseException">
<em class="property">exception </em><tt class="descname">BaseException</tt><a class="headerlink" href="#exceptions.BaseException" title="Permalink to this definition">¶</a></dt>
<dd><p>The base class for all built-in exceptions. It is not meant to be directly
inherited by user-defined classes (for that use <a title="exceptions.Exception" class="reference internal" href="#exceptions.Exception"><tt class="xref docutils literal"><span class="pre">Exception</span></tt></a>). If
<a title="str" class="reference external" href="functions.html#str"><tt class="xref docutils literal"><span class="pre">str()</span></tt></a> or <a title="unicode" class="reference external" href="functions.html#unicode"><tt class="xref docutils literal"><span class="pre">unicode()</span></tt></a> is called on an instance of this class, the
representation of the argument(s) to the instance are returned or the empty
string when there were no arguments. All arguments are stored in <tt class="xref docutils literal"><span class="pre">args</span></tt>
as a tuple.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.Exception">
<em class="property">exception </em><tt class="descname">Exception</tt><a class="headerlink" href="#exceptions.Exception" title="Permalink to this definition">¶</a></dt>
<dd><p>All built-in, non-system-exiting exceptions are derived from this class. All
user-defined exceptions should also be derived from this class.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>Changed to inherit from <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a>.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.StandardError">
<em class="property">exception </em><tt class="descname">StandardError</tt><a class="headerlink" href="#exceptions.StandardError" title="Permalink to this definition">¶</a></dt>
<dd>The base class for all built-in exceptions except <a title="exceptions.StopIteration" class="reference internal" href="#exceptions.StopIteration"><tt class="xref docutils literal"><span class="pre">StopIteration</span></tt></a>,
<a title="exceptions.GeneratorExit" class="reference internal" href="#exceptions.GeneratorExit"><tt class="xref docutils literal"><span class="pre">GeneratorExit</span></tt></a>, <a title="exceptions.KeyboardInterrupt" class="reference internal" href="#exceptions.KeyboardInterrupt"><tt class="xref docutils literal"><span class="pre">KeyboardInterrupt</span></tt></a> and <a title="exceptions.SystemExit" class="reference internal" href="#exceptions.SystemExit"><tt class="xref docutils literal"><span class="pre">SystemExit</span></tt></a>.
<a title="exceptions.StandardError" class="reference internal" href="#exceptions.StandardError"><tt class="xref docutils literal"><span class="pre">StandardError</span></tt></a> itself is derived from <a title="exceptions.Exception" class="reference internal" href="#exceptions.Exception"><tt class="xref docutils literal"><span class="pre">Exception</span></tt></a>.</dd></dl>
<dl class="exception">
<dt id="exceptions.ArithmeticError">
<em class="property">exception </em><tt class="descname">ArithmeticError</tt><a class="headerlink" href="#exceptions.ArithmeticError" title="Permalink to this definition">¶</a></dt>
<dd>The base class for those built-in exceptions that are raised for various
arithmetic errors: <a title="exceptions.OverflowError" class="reference internal" href="#exceptions.OverflowError"><tt class="xref docutils literal"><span class="pre">OverflowError</span></tt></a>, <a title="exceptions.ZeroDivisionError" class="reference internal" href="#exceptions.ZeroDivisionError"><tt class="xref docutils literal"><span class="pre">ZeroDivisionError</span></tt></a>,
<a title="exceptions.FloatingPointError" class="reference internal" href="#exceptions.FloatingPointError"><tt class="xref docutils literal"><span class="pre">FloatingPointError</span></tt></a>.</dd></dl>
<dl class="exception">
<dt id="exceptions.LookupError">
<em class="property">exception </em><tt class="descname">LookupError</tt><a class="headerlink" href="#exceptions.LookupError" title="Permalink to this definition">¶</a></dt>
<dd>The base class for the exceptions that are raised when a key or index used on
a mapping or sequence is invalid: <a title="exceptions.IndexError" class="reference internal" href="#exceptions.IndexError"><tt class="xref docutils literal"><span class="pre">IndexError</span></tt></a>, <a title="exceptions.KeyError" class="reference internal" href="#exceptions.KeyError"><tt class="xref docutils literal"><span class="pre">KeyError</span></tt></a>. This
can be raised directly by <a title="codecs.lookup" class="reference external" href="codecs.html#codecs.lookup"><tt class="xref docutils literal"><span class="pre">codecs.lookup()</span></tt></a>.</dd></dl>
<dl class="exception">
<dt id="exceptions.EnvironmentError">
<em class="property">exception </em><tt class="descname">EnvironmentError</tt><a class="headerlink" href="#exceptions.EnvironmentError" title="Permalink to this definition">¶</a></dt>
<dd><p>The base class for exceptions that can occur outside the Python system:
<a title="exceptions.IOError" class="reference internal" href="#exceptions.IOError"><tt class="xref docutils literal"><span class="pre">IOError</span></tt></a>, <a title="exceptions.OSError" class="reference internal" href="#exceptions.OSError"><tt class="xref docutils literal"><span class="pre">OSError</span></tt></a>. When exceptions of this type are created with a
2-tuple, the first item is available on the instance’s <tt class="xref docutils literal"><span class="pre">errno</span></tt> attribute
(it is assumed to be an error number), and the second item is available on the
<tt class="xref docutils literal"><span class="pre">strerror</span></tt> attribute (it is usually the associated error message). The
tuple itself is also available on the <tt class="xref docutils literal"><span class="pre">args</span></tt> attribute.</p>
<p class="versionadded">
<span class="versionmodified">New in version 1.5.2.</span></p>
<p>When an <a title="exceptions.EnvironmentError" class="reference internal" href="#exceptions.EnvironmentError"><tt class="xref docutils literal"><span class="pre">EnvironmentError</span></tt></a> exception is instantiated with a 3-tuple, the
first two items are available as above, while the third item is available on the
<tt class="xref docutils literal"><span class="pre">filename</span></tt> attribute. However, for backwards compatibility, the
<tt class="xref docutils literal"><span class="pre">args</span></tt> attribute contains only a 2-tuple of the first two constructor
arguments.</p>
<p>The <tt class="xref docutils literal"><span class="pre">filename</span></tt> attribute is <tt class="xref docutils literal"><span class="pre">None</span></tt> when this exception is created with
other than 3 arguments. The <tt class="xref docutils literal"><span class="pre">errno</span></tt> and <tt class="xref docutils literal"><span class="pre">strerror</span></tt> attributes are
also <tt class="xref docutils literal"><span class="pre">None</span></tt> when the instance was created with other than 2 or 3 arguments.
In this last case, <tt class="xref docutils literal"><span class="pre">args</span></tt> contains the verbatim constructor arguments as a
tuple.</p>
</dd></dl>
<p>The following exceptions are the exceptions that are actually raised.</p>
<dl class="exception">
<dt id="exceptions.AssertionError">
<em class="property">exception </em><tt class="descname">AssertionError</tt><a class="headerlink" href="#exceptions.AssertionError" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-331">Raised when an <a class="reference external" href="../reference/simple_stmts.html#assert"><tt class="xref docutils literal"><span class="pre">assert</span></tt></a> statement fails.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.AttributeError">
<em class="property">exception </em><tt class="descname">AttributeError</tt><a class="headerlink" href="#exceptions.AttributeError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when an attribute reference (see <a class="reference external" href="../reference/expressions.html#attribute-references"><em>Attribute references</em></a>) or
assignment fails. (When an object does not support attribute references or
attribute assignments at all, <a title="exceptions.TypeError" class="reference internal" href="#exceptions.TypeError"><tt class="xref docutils literal"><span class="pre">TypeError</span></tt></a> is raised.)</dd></dl>
<dl class="exception">
<dt id="exceptions.EOFError">
<em class="property">exception </em><tt class="descname">EOFError</tt><a class="headerlink" href="#exceptions.EOFError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when one of the built-in functions (<a title="input" class="reference external" href="functions.html#input"><tt class="xref docutils literal"><span class="pre">input()</span></tt></a> or <a title="raw_input" class="reference external" href="functions.html#raw_input"><tt class="xref docutils literal"><span class="pre">raw_input()</span></tt></a>)
hits an end-of-file condition (EOF) without reading any data. (N.B.: the
<a title="file.read" class="reference external" href="stdtypes.html#file.read"><tt class="xref docutils literal"><span class="pre">file.read()</span></tt></a> and <a title="file.readline" class="reference external" href="stdtypes.html#file.readline"><tt class="xref docutils literal"><span class="pre">file.readline()</span></tt></a> methods return an empty string
when they hit EOF.)</dd></dl>
<dl class="exception">
<dt id="exceptions.FloatingPointError">
<em class="property">exception </em><tt class="descname">FloatingPointError</tt><a class="headerlink" href="#exceptions.FloatingPointError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when a floating point operation fails. This exception is always defined,
but can only be raised when Python is configured with the
<em class="xref">--with-fpectl</em> option, or the <tt class="xref docutils literal"><span class="pre">WANT_SIGFPE_HANDLER</span></tt> symbol is
defined in the <tt class="docutils literal"><span class="pre">pyconfig.h</span></tt> file.</dd></dl>
<dl class="exception">
<dt id="exceptions.GeneratorExit">
<em class="property">exception </em><tt class="descname">GeneratorExit</tt><a class="headerlink" href="#exceptions.GeneratorExit" title="Permalink to this definition">¶</a></dt>
<dd><p>Raise when a <a class="reference external" href="../glossary.html#term-generator"><em class="xref">generator</em></a>‘s <tt class="xref docutils literal"><span class="pre">close()</span></tt> method is called. It
directly inherits from <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a> instead of <a title="exceptions.StandardError" class="reference internal" href="#exceptions.StandardError"><tt class="xref docutils literal"><span class="pre">StandardError</span></tt></a> since
it is technically not an error.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.6: </span>Changed to inherit from <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a>.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.IOError">
<em class="property">exception </em><tt class="descname">IOError</tt><a class="headerlink" href="#exceptions.IOError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when an I/O operation (such as a <a class="reference external" href="../reference/simple_stmts.html#print"><tt class="xref docutils literal"><span class="pre">print</span></tt></a> statement, the built-in
<a title="open" class="reference external" href="functions.html#open"><tt class="xref docutils literal"><span class="pre">open()</span></tt></a> function or a method of a file object) fails for an I/O-related
reason, e.g., “file not found” or “disk full”.</p>
<p>This class is derived from <a title="exceptions.EnvironmentError" class="reference internal" href="#exceptions.EnvironmentError"><tt class="xref docutils literal"><span class="pre">EnvironmentError</span></tt></a>. See the discussion above
for more information on exception instance attributes.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.6: </span>Changed <a title="socket.error" class="reference external" href="socket.html#socket.error"><tt class="xref docutils literal"><span class="pre">socket.error</span></tt></a> to use this as a base class.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.ImportError">
<em class="property">exception </em><tt class="descname">ImportError</tt><a class="headerlink" href="#exceptions.ImportError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when an <a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal"><span class="pre">import</span></tt></a> statement fails to find the module definition
or when a <tt class="docutils literal"><span class="pre">from</span> <span class="pre">...</span> <span class="pre">import</span></tt> fails to find a name that is to be imported.</dd></dl>
<dl class="exception">
<dt id="exceptions.IndexError">
<em class="property">exception </em><tt class="descname">IndexError</tt><a class="headerlink" href="#exceptions.IndexError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when a sequence subscript is out of range. (Slice indices are silently
truncated to fall in the allowed range; if an index is not a plain integer,
<a title="exceptions.TypeError" class="reference internal" href="#exceptions.TypeError"><tt class="xref docutils literal"><span class="pre">TypeError</span></tt></a> is raised.)</dd></dl>
<dl class="exception">
<dt id="exceptions.KeyError">
<em class="property">exception </em><tt class="descname">KeyError</tt><a class="headerlink" href="#exceptions.KeyError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when a mapping (dictionary) key is not found in the set of existing keys.</dd></dl>
<dl class="exception">
<dt id="exceptions.KeyboardInterrupt">
<em class="property">exception </em><tt class="descname">KeyboardInterrupt</tt><a class="headerlink" href="#exceptions.KeyboardInterrupt" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when the user hits the interrupt key (normally <tt class="docutils literal"><span class="pre">Control-C</span></tt> or
<tt class="docutils literal"><span class="pre">Delete</span></tt>). During execution, a check for interrupts is made regularly.
Interrupts typed when a built-in function <a title="input" class="reference external" href="functions.html#input"><tt class="xref docutils literal"><span class="pre">input()</span></tt></a> or <a title="raw_input" class="reference external" href="functions.html#raw_input"><tt class="xref docutils literal"><span class="pre">raw_input()</span></tt></a> is
waiting for input also raise this exception. The exception inherits from
<a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a> so as to not be accidentally caught by code that catches
<a title="exceptions.Exception" class="reference internal" href="#exceptions.Exception"><tt class="xref docutils literal"><span class="pre">Exception</span></tt></a> and thus prevent the interpreter from exiting.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>Changed to inherit from <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a>.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.MemoryError">
<em class="property">exception </em><tt class="descname">MemoryError</tt><a class="headerlink" href="#exceptions.MemoryError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when an operation runs out of memory but the situation may still be
rescued (by deleting some objects). The associated value is a string indicating
what kind of (internal) operation ran out of memory. Note that because of the
underlying memory management architecture (C’s <tt class="xref docutils literal"><span class="pre">malloc()</span></tt> function), the
interpreter may not always be able to completely recover from this situation; it
nevertheless raises an exception so that a stack traceback can be printed, in
case a run-away program was the cause.</dd></dl>
<dl class="exception">
<dt id="exceptions.NameError">
<em class="property">exception </em><tt class="descname">NameError</tt><a class="headerlink" href="#exceptions.NameError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when a local or global name is not found. This applies only to
unqualified names. The associated value is an error message that includes the
name that could not be found.</dd></dl>
<dl class="exception">
<dt id="exceptions.NotImplementedError">
<em class="property">exception </em><tt class="descname">NotImplementedError</tt><a class="headerlink" href="#exceptions.NotImplementedError" title="Permalink to this definition">¶</a></dt>
<dd><p>This exception is derived from <a title="exceptions.RuntimeError" class="reference internal" href="#exceptions.RuntimeError"><tt class="xref docutils literal"><span class="pre">RuntimeError</span></tt></a>. In user defined base
classes, abstract methods should raise this exception when they require derived
classes to override the method.</p>
<p class="versionadded">
<span class="versionmodified">New in version 1.5.2.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.OSError">
<em class="property">exception </em><tt class="descname">OSError</tt><a class="headerlink" href="#exceptions.OSError" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-332">This exception is derived from <a title="exceptions.EnvironmentError" class="reference internal" href="#exceptions.EnvironmentError"><tt class="xref docutils literal"><span class="pre">EnvironmentError</span></tt></a>. It is raised when a
function returns a system-related error (not for illegal argument types or
other incidental errors). The <tt class="xref docutils literal"><span class="pre">errno</span></tt> attribute is a numeric error
code from <tt class="xref docutils literal"><span class="pre">errno</span></tt>, and the <tt class="xref docutils literal"><span class="pre">strerror</span></tt> attribute is the
corresponding string, as would be printed by the C function <tt class="xref docutils literal"><span class="pre">perror()</span></tt>.
See the module <a title="Standard errno system symbols." class="reference external" href="errno.html#module-errno"><tt class="xref docutils literal"><span class="pre">errno</span></tt></a>, which contains names for the error codes defined
by the underlying operating system.</p>
<p>For exceptions that involve a file system path (such as <tt class="xref docutils literal"><span class="pre">chdir()</span></tt> or
<tt class="xref docutils literal"><span class="pre">unlink()</span></tt>), the exception instance will contain a third attribute,
<tt class="xref docutils literal"><span class="pre">filename</span></tt>, which is the file name passed to the function.</p>
<p class="versionadded">
<span class="versionmodified">New in version 1.5.2.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.OverflowError">
<em class="property">exception </em><tt class="descname">OverflowError</tt><a class="headerlink" href="#exceptions.OverflowError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when the result of an arithmetic operation is too large to be
represented. This cannot occur for long integers (which would rather raise
<a title="exceptions.MemoryError" class="reference internal" href="#exceptions.MemoryError"><tt class="xref docutils literal"><span class="pre">MemoryError</span></tt></a> than give up) and for most operations with plain integers,
which return a long integer instead. Because of the lack of standardization
of floating point exception handling in C, most floating point operations
also aren’t checked.</dd></dl>
<dl class="exception">
<dt id="exceptions.ReferenceError">
<em class="property">exception </em><tt class="descname">ReferenceError</tt><a class="headerlink" href="#exceptions.ReferenceError" title="Permalink to this definition">¶</a></dt>
<dd><p>This exception is raised when a weak reference proxy, created by the
<a title="weakref.proxy" class="reference external" href="weakref.html#weakref.proxy"><tt class="xref docutils literal"><span class="pre">weakref.proxy()</span></tt></a> function, is used to access an attribute of the referent
after it has been garbage collected. For more information on weak references,
see the <a title="Support for weak references and weak dictionaries." class="reference external" href="weakref.html#module-weakref"><tt class="xref docutils literal"><span class="pre">weakref</span></tt></a> module.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2: </span>Previously known as the <a title="weakref.ReferenceError" class="reference external" href="weakref.html#weakref.ReferenceError"><tt class="xref docutils literal"><span class="pre">weakref.ReferenceError</span></tt></a> exception.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.RuntimeError">
<em class="property">exception </em><tt class="descname">RuntimeError</tt><a class="headerlink" href="#exceptions.RuntimeError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when an error is detected that doesn’t fall in any of the other
categories. The associated value is a string indicating what precisely went
wrong. (This exception is mostly a relic from a previous version of the
interpreter; it is not used very much any more.)</dd></dl>
<dl class="exception">
<dt id="exceptions.StopIteration">
<em class="property">exception </em><tt class="descname">StopIteration</tt><a class="headerlink" href="#exceptions.StopIteration" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised by an <a class="reference external" href="../glossary.html#term-iterator"><em class="xref">iterator</em></a>‘s <a title="iterator.next" class="reference external" href="stdtypes.html#iterator.next"><tt class="xref docutils literal"><span class="pre">next()</span></tt></a> method to signal that
there are no further values. This is derived from <a title="exceptions.Exception" class="reference internal" href="#exceptions.Exception"><tt class="xref docutils literal"><span class="pre">Exception</span></tt></a> rather
than <a title="exceptions.StandardError" class="reference internal" href="#exceptions.StandardError"><tt class="xref docutils literal"><span class="pre">StandardError</span></tt></a>, since this is not considered an error in its
normal application.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.SyntaxError">
<em class="property">exception </em><tt class="descname">SyntaxError</tt><a class="headerlink" href="#exceptions.SyntaxError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when the parser encounters a syntax error. This may occur in an
<a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal"><span class="pre">import</span></tt></a> statement, in an <a class="reference external" href="../reference/simple_stmts.html#exec"><tt class="xref docutils literal"><span class="pre">exec</span></tt></a> statement, in a call to the
built-in function <a title="eval" class="reference external" href="functions.html#eval"><tt class="xref docutils literal"><span class="pre">eval()</span></tt></a> or <a title="input" class="reference external" href="functions.html#input"><tt class="xref docutils literal"><span class="pre">input()</span></tt></a>, or when reading the initial
script or standard input (also interactively).</p>
<p>Instances of this class have attributes <tt class="xref docutils literal"><span class="pre">filename</span></tt>, <tt class="xref docutils literal"><span class="pre">lineno</span></tt>,
<tt class="xref docutils literal"><span class="pre">offset</span></tt> and <tt class="xref docutils literal"><span class="pre">text</span></tt> for easier access to the details. <a title="str" class="reference external" href="functions.html#str"><tt class="xref docutils literal"><span class="pre">str()</span></tt></a>
of the exception instance returns only the message.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.SystemError">
<em class="property">exception </em><tt class="descname">SystemError</tt><a class="headerlink" href="#exceptions.SystemError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when the interpreter finds an internal error, but the situation does not
look so serious to cause it to abandon all hope. The associated value is a
string indicating what went wrong (in low-level terms).</p>
<p>You should report this to the author or maintainer of your Python interpreter.
Be sure to report the version of the Python interpreter (<tt class="docutils literal"><span class="pre">sys.version</span></tt>; it is
also printed at the start of an interactive Python session), the exact error
message (the exception’s associated value) and if possible the source of the
program that triggered the error.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.SystemExit">
<em class="property">exception </em><tt class="descname">SystemExit</tt><a class="headerlink" href="#exceptions.SystemExit" title="Permalink to this definition">¶</a></dt>
<dd><p>This exception is raised by the <a title="sys.exit" class="reference external" href="sys.html#sys.exit"><tt class="xref docutils literal"><span class="pre">sys.exit()</span></tt></a> function. When it is not
handled, the Python interpreter exits; no stack traceback is printed. If the
associated value is a plain integer, it specifies the system exit status (passed
to C’s <tt class="xref docutils literal"><span class="pre">exit()</span></tt> function); if it is <tt class="xref docutils literal"><span class="pre">None</span></tt>, the exit status is zero; if
it has another type (such as a string), the object’s value is printed and the
exit status is one.</p>
<p>Instances have an attribute <tt class="xref docutils literal"><span class="pre">code</span></tt> which is set to the proposed exit
status or error message (defaulting to <tt class="xref docutils literal"><span class="pre">None</span></tt>). Also, this exception derives
directly from <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a> and not <a title="exceptions.StandardError" class="reference internal" href="#exceptions.StandardError"><tt class="xref docutils literal"><span class="pre">StandardError</span></tt></a>, since it is not
technically an error.</p>
<p>A call to <a title="sys.exit" class="reference external" href="sys.html#sys.exit"><tt class="xref docutils literal"><span class="pre">sys.exit()</span></tt></a> is translated into an exception so that clean-up
handlers (<a class="reference external" href="../reference/compound_stmts.html#finally"><tt class="xref docutils literal"><span class="pre">finally</span></tt></a> clauses of <a class="reference external" href="../reference/compound_stmts.html#try"><tt class="xref docutils literal"><span class="pre">try</span></tt></a> statements) can be
executed, and so that a debugger can execute a script without running the risk
of losing control. The <a title="os._exit" class="reference external" href="os.html#os._exit"><tt class="xref docutils literal"><span class="pre">os._exit()</span></tt></a> function can be used if it is
absolutely positively necessary to exit immediately (for example, in the child
process after a call to <tt class="xref docutils literal"><span class="pre">fork()</span></tt>).</p>
<p>The exception inherits from <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a> instead of <a title="exceptions.StandardError" class="reference internal" href="#exceptions.StandardError"><tt class="xref docutils literal"><span class="pre">StandardError</span></tt></a>
or <a title="exceptions.Exception" class="reference internal" href="#exceptions.Exception"><tt class="xref docutils literal"><span class="pre">Exception</span></tt></a> so that it is not accidentally caught by code that catches
<a title="exceptions.Exception" class="reference internal" href="#exceptions.Exception"><tt class="xref docutils literal"><span class="pre">Exception</span></tt></a>. This allows the exception to properly propagate up and cause
the interpreter to exit.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>Changed to inherit from <a title="exceptions.BaseException" class="reference internal" href="#exceptions.BaseException"><tt class="xref docutils literal"><span class="pre">BaseException</span></tt></a>.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.TypeError">
<em class="property">exception </em><tt class="descname">TypeError</tt><a class="headerlink" href="#exceptions.TypeError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when an operation or function is applied to an object of inappropriate
type. The associated value is a string giving details about the type mismatch.</dd></dl>
<dl class="exception">
<dt id="exceptions.UnboundLocalError">
<em class="property">exception </em><tt class="descname">UnboundLocalError</tt><a class="headerlink" href="#exceptions.UnboundLocalError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when a reference is made to a local variable in a function or method, but
no value has been bound to that variable. This is a subclass of
<a title="exceptions.NameError" class="reference internal" href="#exceptions.NameError"><tt class="xref docutils literal"><span class="pre">NameError</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.0.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.UnicodeError">
<em class="property">exception </em><tt class="descname">UnicodeError</tt><a class="headerlink" href="#exceptions.UnicodeError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when a Unicode-related encoding or decoding error occurs. It is a
subclass of <a title="exceptions.ValueError" class="reference internal" href="#exceptions.ValueError"><tt class="xref docutils literal"><span class="pre">ValueError</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.0.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.UnicodeEncodeError">
<em class="property">exception </em><tt class="descname">UnicodeEncodeError</tt><a class="headerlink" href="#exceptions.UnicodeEncodeError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when a Unicode-related error occurs during encoding. It is a subclass of
<a title="exceptions.UnicodeError" class="reference internal" href="#exceptions.UnicodeError"><tt class="xref docutils literal"><span class="pre">UnicodeError</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.UnicodeDecodeError">
<em class="property">exception </em><tt class="descname">UnicodeDecodeError</tt><a class="headerlink" href="#exceptions.UnicodeDecodeError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when a Unicode-related error occurs during decoding. It is a subclass of
<a title="exceptions.UnicodeError" class="reference internal" href="#exceptions.UnicodeError"><tt class="xref docutils literal"><span class="pre">UnicodeError</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.UnicodeTranslateError">
<em class="property">exception </em><tt class="descname">UnicodeTranslateError</tt><a class="headerlink" href="#exceptions.UnicodeTranslateError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when a Unicode-related error occurs during translating. It is a subclass
of <a title="exceptions.UnicodeError" class="reference internal" href="#exceptions.UnicodeError"><tt class="xref docutils literal"><span class="pre">UnicodeError</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.ValueError">
<em class="property">exception </em><tt class="descname">ValueError</tt><a class="headerlink" href="#exceptions.ValueError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when a built-in operation or function receives an argument that has the
right type but an inappropriate value, and the situation is not described by a
more precise exception such as <a title="exceptions.IndexError" class="reference internal" href="#exceptions.IndexError"><tt class="xref docutils literal"><span class="pre">IndexError</span></tt></a>.</dd></dl>
<dl class="exception">
<dt id="exceptions.VMSError">
<em class="property">exception </em><tt class="descname">VMSError</tt><a class="headerlink" href="#exceptions.VMSError" title="Permalink to this definition">¶</a></dt>
<dd>Only available on VMS. Raised when a VMS-specific error occurs.</dd></dl>
<dl class="exception">
<dt id="exceptions.WindowsError">
<em class="property">exception </em><tt class="descname">WindowsError</tt><a class="headerlink" href="#exceptions.WindowsError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when a Windows-specific error occurs or when the error number does not
correspond to an <tt class="xref docutils literal"><span class="pre">errno</span></tt> value. The <tt class="xref docutils literal"><span class="pre">winerror</span></tt> and
<tt class="xref docutils literal"><span class="pre">strerror</span></tt> values are created from the return values of the
<tt class="xref docutils literal"><span class="pre">GetLastError()</span></tt> and <tt class="xref docutils literal"><span class="pre">FormatMessage()</span></tt> functions from the Windows
Platform API. The <tt class="xref docutils literal"><span class="pre">errno</span></tt> value maps the <tt class="xref docutils literal"><span class="pre">winerror</span></tt> value to
corresponding <tt class="docutils literal"><span class="pre">errno.h</span></tt> values. This is a subclass of <a title="exceptions.OSError" class="reference internal" href="#exceptions.OSError"><tt class="xref docutils literal"><span class="pre">OSError</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.0.</span></p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.5: </span>Previous versions put the <tt class="xref docutils literal"><span class="pre">GetLastError()</span></tt> codes into <tt class="xref docutils literal"><span class="pre">errno</span></tt>.</p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.ZeroDivisionError">
<em class="property">exception </em><tt class="descname">ZeroDivisionError</tt><a class="headerlink" href="#exceptions.ZeroDivisionError" title="Permalink to this definition">¶</a></dt>
<dd>Raised when the second argument of a division or modulo operation is zero. The
associated value is a string indicating the type of the operands and the
operation.</dd></dl>
<p>The following exceptions are used as warning categories; see the <a title="Issue warning messages and control their disposition." class="reference external" href="warnings.html#module-warnings"><tt class="xref docutils literal"><span class="pre">warnings</span></tt></a>
module for more information.</p>
<dl class="exception">
<dt id="exceptions.Warning">
<em class="property">exception </em><tt class="descname">Warning</tt><a class="headerlink" href="#exceptions.Warning" title="Permalink to this definition">¶</a></dt>
<dd>Base class for warning categories.</dd></dl>
<dl class="exception">
<dt id="exceptions.UserWarning">
<em class="property">exception </em><tt class="descname">UserWarning</tt><a class="headerlink" href="#exceptions.UserWarning" title="Permalink to this definition">¶</a></dt>
<dd>Base class for warnings generated by user code.</dd></dl>
<dl class="exception">
<dt id="exceptions.DeprecationWarning">
<em class="property">exception </em><tt class="descname">DeprecationWarning</tt><a class="headerlink" href="#exceptions.DeprecationWarning" title="Permalink to this definition">¶</a></dt>
<dd>Base class for warnings about deprecated features.</dd></dl>
<dl class="exception">
<dt id="exceptions.PendingDeprecationWarning">
<em class="property">exception </em><tt class="descname">PendingDeprecationWarning</tt><a class="headerlink" href="#exceptions.PendingDeprecationWarning" title="Permalink to this definition">¶</a></dt>
<dd>Base class for warnings about features which will be deprecated in the future.</dd></dl>
<dl class="exception">
<dt id="exceptions.SyntaxWarning">
<em class="property">exception </em><tt class="descname">SyntaxWarning</tt><a class="headerlink" href="#exceptions.SyntaxWarning" title="Permalink to this definition">¶</a></dt>
<dd>Base class for warnings about dubious syntax</dd></dl>
<dl class="exception">
<dt id="exceptions.RuntimeWarning">
<em class="property">exception </em><tt class="descname">RuntimeWarning</tt><a class="headerlink" href="#exceptions.RuntimeWarning" title="Permalink to this definition">¶</a></dt>
<dd>Base class for warnings about dubious runtime behavior.</dd></dl>
<dl class="exception">
<dt id="exceptions.FutureWarning">
<em class="property">exception </em><tt class="descname">FutureWarning</tt><a class="headerlink" href="#exceptions.FutureWarning" title="Permalink to this definition">¶</a></dt>
<dd>Base class for warnings about constructs that will change semantically in the
future.</dd></dl>
<dl class="exception">
<dt id="exceptions.ImportWarning">
<em class="property">exception </em><tt class="descname">ImportWarning</tt><a class="headerlink" href="#exceptions.ImportWarning" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for warnings about probable mistakes in module imports.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>
<dl class="exception">
<dt id="exceptions.UnicodeWarning">
<em class="property">exception </em><tt class="descname">UnicodeWarning</tt><a class="headerlink" href="#exceptions.UnicodeWarning" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for warnings related to Unicode.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>
<div class="section" id="exception-hierarchy">
<h2>6.1. Exception hierarchy<a class="headerlink" href="#exception-hierarchy" title="Permalink to this headline">¶</a></h2>
<p>The class hierarchy for built-in exceptions is:</p>
<div class="highlight-python"><pre>BaseException
+-- SystemExit
+-- KeyboardInterrupt
+-- GeneratorExit
+-- Exception
+-- StopIteration
+-- StandardError
| +-- BufferError
| +-- ArithmeticError
| | +-- FloatingPointError
| | +-- OverflowError
| | +-- ZeroDivisionError
| +-- AssertionError
| +-- AttributeError
| +-- EnvironmentError
| | +-- IOError
| | +-- OSError
| | +-- WindowsError (Windows)
| | +-- VMSError (VMS)
| +-- EOFError
| +-- ImportError
| +-- LookupError
| | +-- IndexError
| | +-- KeyError
| +-- MemoryError
| +-- NameError
| | +-- UnboundLocalError
| +-- ReferenceError
| +-- RuntimeError
| | +-- NotImplementedError
| +-- SyntaxError
| | +-- IndentationError
| | +-- TabError
| +-- SystemError
| +-- TypeError
| +-- ValueError
| +-- UnicodeError
| +-- UnicodeDecodeError
| +-- UnicodeEncodeError
| +-- UnicodeTranslateError
+-- Warning
+-- DeprecationWarning
+-- PendingDeprecationWarning
+-- RuntimeWarning
+-- SyntaxWarning
+-- UserWarning
+-- FutureWarning
+-- ImportWarning
+-- UnicodeWarning
+-- BytesWarning
</pre>
</div>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
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<li><a class="reference external" href="#">6. Built-in Exceptions</a><ul>
<li><a class="reference external" href="#exception-hierarchy">6.1. Exception hierarchy</a></li>
</ul>
</li>
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