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<H3><A NAME="SECTION004294000000000000000"> </A>
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2.2.9.4 Methods
</H3>
<a name="l2h-181"> </a>
<P>
Methods are functions that are called using the attribute notation.
There are two flavors: built-in methods (such as <tt class="method">append()</tt> on
lists) and class instance methods. Built-in methods are described
with the types that support them.
<P>
The implementation adds two special read-only attributes to class
instance methods: <code><var>m</var>.im_self</code> is the object on which the
method operates, and <code><var>m</var>.im_func</code> is the function
implementing the method. Calling <code><var>m</var>(<var>arg-1</var>,
<var>arg-2</var>, ..., <var>arg-n</var>)</code> is completely equivalent to
calling <code><var>m</var>.im_func(<var>m</var>.im_self, <var>arg-1</var>,
<var>arg-2</var>, ..., <var>arg-n</var>)</code>.
<P>
Class instance methods are either <i>bound</i> or <i>unbound</i>,
referring to whether the method was accessed through an instance or a
class, respectively. When a method is unbound, its <code>im_self</code>
attribute will be <code>None</code> and if called, an explicit <code>self</code>
object must be passed as the first argument. In this case,
<code>self</code> must be an instance of the unbound method's class (or a
subclass of that class), otherwise a <code>TypeError</code> is raised.
<P>
Like function objects, methods objects support getting
arbitrary attributes. However, since method attributes are actually
stored on the underlying function object (<code>meth.im_func</code>),
setting method attributes on either bound or unbound methods is
disallowed. Attempting to set a method attribute results in a
<code>TypeError</code> being raised. In order to set a method attribute,
you need to explicitly set it on the underlying function object:
<P>
<dl><dd><pre class="verbatim">
class C:
def method(self):
pass
c = C()
c.method.im_func.whoami = 'my name is c'
</pre></dl>
<P>
See the <em class="citetitle"><a
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title="Python Reference Manual"
>Python Reference Manual</a></em> for more
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<span class="release-info">Release 2.2, documentation updated on December 21, 2001.</span>
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