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 like below:

def func1(nums):
    nums = [4,5,6]

nums = [1,2,3]
func1(nums)
print nums # print [1,2,3]

def func2(nums):
    nums[0] = 4
    nums[1] = 5
    nums[2] = 6

nums = [1,2,3]
func2(nums)
print nums # print [4,5,6]

After trying func2, I realized that I can always access global list in a function if I specify the index:

def func3(nums):
    nums[:] = [4,5,6]

nums = [1,2,3]
func3(nums)
print nums # print [4,5,6]

Is it because Python automatically go trying to match a global variable if a function variable is used before definition?

Answer 1

I understand that I can use global statement to access global variables

Your understanding is wrong. You can always access a global variable as long as you don't have a local variable of the same name. You only need the global statement when you are going to change what object a variable name refers to. In your func2, you are not doing that; you are only changing the contents of the object. nums still refers to the same list.