def add_list(p):
p = p + [1]
p1 = [1, 2, 3]
add_list(p1)
print p1
res:[1, 2, 3]
BUT
def add_list(p):
p += [1]
p1 = [1, 2, 3]
add_list(p1)
print p1
res:[1, 2, 3, 1]
I don't know why, can someone explain this? What's the main difference between them?