Python: Modify Global list inside a function

Question

First of all, I understand that I can use global statement to access global variables. But somehow I was able to modify a global list without global

Answer 1

It is of concept based on mutable and immutable objects in Python. In your case, for example:

a=[1,2]
def myfn():
    a=[3,4]
    print id(a)

>>>id(a)
3065250924L
>>>myfn()
3055359596

It is clear both are different objects. Now:

a=[1,2]
def myfn():
    a[:] =[3,4]
    print id(a)

>>>id(a)
3055358572
>>>myfn()
3055358572

That means it is same variable using in local and global scope.