wtf.py

class A(object):
    def hook(self, f):
        atime = 0
        def intime(*args):
            print atime
            atime += 1
            return f(*args)
        return intime

>>> f = A().hook(lambda b: b + 1)
>>> f(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 5, in intime
UnboundLocalError: local variable 'atime' referenced before assignment
>>>

wtf3.py

#!/usr/bin/env python3

class A(object):
    def hook(self, f):
        atime = 0
        def intime(*args):
            nonlocal atime
            print(atime)
            atime += 1
            return f(*args)
        return intime

f = A().hook(lambda b: b + 1)

# works as expected
for i in range(10):
    f(i)