Default function arguments have global scope leading to unexpected behavior

Question

I have a simple python question. Consider the following code.

import random

def int_list(local_list=[]):
    local_list.append(random.randint(0,1000))
    return local_list

for i in range(5):
    print(int_list())

Under both python2 and python3 the result is:

>> [828]
>> [828, 268]
>> [828, 268, 999]
>> [828, 268, 999, 471]
>> [828, 268, 999, 471, 847]

I would have expected the following result instead:

>> [828]
>> [268]
>> [999]
>> [471]
>> [847]

Apparently the object used to instantiate local_list has global scope and is the same for every invocation. Not only does this surprise me, but it also seems like incorrect or at least undesirable behavior. I assume this question has been raised before. Can someone point me to a rationale?