Python Language User-Defined Methods Creating user-defined method objects
Example
User-defined method objects may be created when getting an attribute of a class (perhaps via an instance of that class), if that attribute is a user-defined function object, an unbound user-defined method object, or a class method object.
class A(object):
# func: A user-defined function object
#
# Note that func is a function object when it's defined,
# and an unbound method object when it's retrieved.
def func(self):
pass
# classMethod: A class method
@classmethod
def classMethod(self):
pass
class B(object):
# unboundMeth: A unbound user-defined method object
#
# Parent.func is an unbound user-defined method object here,
# because it's retrieved.
unboundMeth = A.func
a = A()
b = B()
print A.func
# output: <unbound method A.func>
print a.func
# output: <bound method A.func of <__main__.A object at 0x10e9ab910>>
print B.unboundMeth
# output: <unbound method A.func>
print b.unboundMeth
# output: <unbound method A.func>
print A.classMethod
# output: <bound method type.classMethod of <class '__main__.A'>>
print a.classMethod
# output: <bound method type.classMethod of <class '__main__.A'>>
When the attribute is a user-defined method object, a new method object is only created if the class from which it is being retrieved is the same as, or a derived class of, the class stored in the original method object; otherwise, the original method object is used as it is.
# Parent: The class stored in the original method object
class Parent(object):
# func: The underlying function of original method object
def func(self):
pass
func2 = func
# Child: A derived class of Parent
class Child(Parent):
func = Parent.func
# AnotherClass: A different class, neither subclasses nor subclassed
class AnotherClass(object):
func = Parent.func
print Parent.func is Parent.func # False, new object created
print Parent.func2 is Parent.func2 # False, new object created
print Child.func is Child.func # False, new object created
print AnotherClass.func is AnotherClass.func # True, original object used
