What is the difference between fun1 and fun2 ? Why arr in fun1 have old memory of first call while calling second time?

Question

#Code:
def fun1(val, arr=[]):
for i in val:
arr.append(i)
return len(arr)

def fun2(val):
arr = []
for i in val:
arr.append(i)
return len(arr)

print(fun1(range(4))+fun1(range(5)))

print(fun2(range(4))+fun2(range(5)))

#Output:
13
9

Answer 1

In fun2 arr = [] resets the variable arr to an empty list each time the function is called. In fun1 arr is a parameter that will have a default of an empty list if arr is not already set or a value has not been previously passed. If you pass an empty list [] with the second call to fun1 the result will be the same as it is with fun2.
print(fun1(range(4))+fun1(range(5), []))

Or change fun1 as follows:

def fun1(val, arr=None):
if arr == None:
arr = []
for i in val:
arr.append(i)
return len(arr)

http://docs.python-guide.org/en/latest/writing/gotchas/

Answer 2

@ChaoticDawg, thank you👍