Ok, again, this is not something you should normally do, this is for informational purposes only.
Where Python looks for a method on an instance object is determined by the __mro__
attribute of the class which defines that object (the M ethod R esolution O rder attribute). Thus, if we could modify the __mro__
of Person
, we’d get the desired behaviour. Something like:
setattr(Person, '__mro__', (Person, Friendly, object))
The problem is that __mro__
is a readonly attribute, and thus setattr won’t work. Maybe if you’re a Python guru there’s a way around that, but clearly I fall short of guru status as I cannot think of one.
A possible workaround is to simply redefine the class:
def modify_Person_to_be_friendly():
# so that we're modifying the global identifier 'Person'
global Person
# now just redefine the class using type(), specifying that the new
# class should inherit from Friendly and have all attributes from
# our old Person class
Person = type('Person', (Friendly,), dict(Person.__dict__))
def main():
modify_Person_to_be_friendly()
p = Person()
p.hello() # works!
What this doesn’t do is modify any previously created Person
instances to have the hello()
method. For example (just modifying main()
):
def main():
oldperson = Person()
ModifyPersonToBeFriendly()
p = Person()
p.hello()
# works! But:
oldperson.hello()
# does not
If the details of the type
call aren’t clear, then read e-satis’ excellent answer on ‘What is a metaclass in Python?’.