What is the output?

Question

n = 5
ar1 = ar2 = []
for i in range(n):
ar1.append(0)
ar2.append (0)
print(len(ar1))

Answer 1

The unexpected result is 10 because ar1 and ar2 are two lists linked to the same object. So at every loop both lists are expanded by 2 elements.
If you want to define 2 differents lists you must write
ar1,ar2 = [],[]
instead of
ar1 = ar2 = []