2.1.7.4 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 and setting arbitrary attributes. However, the attributes are actually stored on the underlying function object (i.e. meth.im_func). To avoid surprising behavior, a TypeError is raised when an attempt is made to set an attribute on a bound method. It is legal to get a bound method's attribute (the underlying function's attribute is returned), and it is also legal to set or get an unbound method's attribute. For example:

class C:
    def method(self):
        pass

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

If bound method attribute setting was allowed, c.method.whoami would return ``my name is d''.

See the Python Reference Manual for more information.

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