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<H1><A NAME="SECTION009600000000000000000"></A><A NAME="class"></A>
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7.6 Class definitions
</H1>
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A class definition defines a class object (see section&nbsp;<A href="types.html#types">3.2</A>):
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    <td><a id='tok-classdef' xml:id='tok-classdef'>classdef</a></td>
    <td>::=</td>
    <td>"class" <a class='grammartoken' href="class.html#tok-classname">classname</a> [<a class='grammartoken' href="class.html#tok-inheritance">inheritance</a>] ":"
              <a class='grammartoken' href="compound.html#tok-suite">suite</a></td></tr>
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    <td><a id='tok-inheritance' xml:id='tok-inheritance'>inheritance</a></td>
    <td>::=</td>
    <td>"(" <a class='grammartoken' href="exprlists.html#tok-expression_list">expression_list</a> ")"</td></tr>
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    <td><a id='tok-classname' xml:id='tok-classname'>classname</a></td>
    <td>::=</td>
    <td><a class='grammartoken' href="identifiers.html#tok-identifier">identifier</a></td></tr>
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<a class="grammar-footer"
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A class definition is an executable statement.  It first evaluates the
inheritance list, if present.  Each item in the inheritance list
should evaluate to a class object or class type which allows
subclassing.  The class's suite is then executed
in a new execution frame (see section&nbsp;<A href="naming.html#naming">4.1</A>), using a newly
created local namespace and the original global namespace.
(Usually, the suite contains only function definitions.)  When the
class's suite finishes execution, its execution frame is discarded but
its local namespace is saved.  A class object is then created using
the inheritance list for the base classes and the saved local
namespace for the attribute dictionary.  The class name is bound to this
class object in the original local namespace.
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<P>
<strong>Programmer's note:</strong> Variables defined in the class definition
are class variables; they are shared by all instances.  To define
instance variables, they must be given a value in the
<tt class="method">__init__()</tt> method or in another method.  Both class and
instance variables are accessible through the notation
``<code>self.name</code>'', and an instance variable hides a class variable
with the same name when accessed in this way.  Class variables with
immutable values can be used as defaults for instance variables.
For new-style classes, descriptors can be used to create instance
variables with different implementation details.

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