monkey-patching python an instance method [duplicate]

Answer 1

Doh!

>>> import types
>>> s.make = types.MethodType(times_eight, s, Simple)
>>> s.make(10)
80

Answer 2

You can create a new instance method out of times_eight by using its __get__ special method:

>>> class Simple(object):
...     def make(self, arg):
...         return arg * 2
...
>>> s = Simple()
>>> def times_eight(self, arg):
...     return arg * 8
...
>>> s.make = times_eight.__get__(s, Simple)
>>> s.make(10)
80
>>> type(s.make)
<type 'instancemethod'>
>>>

Answer 3

Methods only get the self arg passed automatically when received from the class (not from the instance dict), so you'll need to pass an 1-arg function there:

s.make = lambda arg: times_eight(s, arg)

(You can simplify that with functools.partial.)