Aaj Kaal
2020-11-30 22:36:45
The reason is list is a mutable object. On the first call a is initialized and in subsequent calls it is referenced. int and str are immmutable as you can see from below:
>>> str1 = 'hello'
>>> id(str1)
1900958690736
>>> str1 = 'how r u'
>>> id(str1) # is a different string now
1900958712176
In order to achieve what you are looking for you can use:
def f(b, a=None):
if not a:
a = []
a.append(b)
print('a : ', a)
f(1) # a : [1]
f(2) # a : [2]
thanks a lot! your answer is PERFECT