Adding a Method to an Existing Object Instance

Question

I\'ve read that it is possible to add a method to an existing object (i.e., not in the class definition) in Python.

I understand that it\'s not always good to do so

Answer 1

There are at least two ways for attach a method to an instance without types.MethodType:

>>> class A:
...  def m(self):
...   print 'im m, invoked with: ', self

>>> a = A()
>>> a.m()
im m, invoked with:  <__main__.A instance at 0x973ec6c>
>>> a.m
>
>>> 
>>> def foo(firstargument):
...  print 'im foo, invoked with: ', firstargument

>>> foo

1:

>>> a.foo = foo.__get__(a, A) # or foo.__get__(a, type(a))
>>> a.foo()
im foo, invoked with:  <__main__.A instance at 0x973ec6c>
>>> a.foo
>

2:

>>> instancemethod = type(A.m)
>>> instancemethod

>>> a.foo2 = instancemethod(foo, a, type(a))
>>> a.foo2()
im foo, invoked with:  <__main__.A instance at 0x973ec6c>
>>> a.foo2
>

Useful links:
Data model - invoking descriptors
Descriptor HowTo Guide - invoking descriptors