Double class definitions in python

Question

I just realized the following works. How come it works? What are the details of this? What happens if the class definitions differ?

class A(object):
    pass

class A(object):
    pass

Answer 1

The second definition overrides the first definition. It's not different from simple variables:

>>> i = 2
>>> i = 3
>>> print(i)
3

Same holds true for functions: you just re-define it.

>>> def f(): return 1
... 
>>> def f(): return 2
... 
>>> f()
2

Python doesn't enforce the uniqueness of the object names (ie doesn't crash with "...already defined"). It also doesn't care about the internals: first class definition might have different methods from the second class definition. The order is the only thing that matters here.

Answer 2

The second definition gets overriden.

 $  cat test.py 
class A(object):
    def __str__(self):
        return 'first A'

class A(object):
    def __str__(self):
        return 'second A'

a1 = A()
print(a1)

 $  python test.py 
second A