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2.2.9.4 Methods

Methods are functions that are called using the attribute notation. There are two flavors: built-in methods (such as `append()` on lists) and class instance methods. Built-in methods are described with the types that support them.

The implementation adds two special read-only attributes to class instance methods: `m.im_self` is the object on which the method operates, and `m.im_func` is the function implementing the method. Calling `m(arg-1, arg-2, ..., arg-n)` is completely equivalent to calling `m.im_func(m.im_self, arg-1, arg-2, ..., arg-n)`.

Class instance methods are either bound or unbound, referring to whether the method was accessed through an instance or a class, respectively. When a method is unbound, its `im_self` attribute will be `None` and if called, an explicit `self` object must be passed as the first argument. In this case, `self` must be an instance of the unbound method's class (or a subclass of that class), otherwise a `TypeError` is raised.

Like function objects, methods objects support getting arbitrary attributes. However, since method attributes are actually stored on the underlying function object (`meth.im_func`), setting method attributes on either bound or unbound methods is disallowed. Attempting to set a method attribute results in a `TypeError` being raised. In order to set a method attribute, you need to explicitly set it on the underlying function object:

    class C:
        def method(self):
            pass

    c = C()
    c.method.im_func.whoami = 'my name is c'

See the Python Reference Manual for more information.