Overriding the instance next function

Question

I'm trying to override an object's next function using the code below (python 2.7).

When the object's next method is called directly, the new function is invoked. However when I call the builtin next() function on my object (which, according to the docs, should call the instance's next method), the ORIGINAL function is invoked.

Can someone explain this behaviour?

class Test(object):
    def __iter__(self):
        return self
    def next(self):
        return 1

test = Test()
def new_next(self):
    return 2

test.next = type(test.__class__.next)(new_next, test, test.__class__)
print test.next() # 2
print next(test) # 1

Answer 1

If I'm reading this source correctly it seems like the iterator is set when the class is defined. I might read it wrong though. I'm guessing it's for fast lookup of the next function (setting it as a slot) since it's used in loops etc.

Given that, the following seems to do what you're after:

>>> test.__class__.next = type(test.__class__.next)(new_next, test, test.__class__)
>>> next(test)
2