sum list

a = [1, 2, 3]
b = [4, 5, 6]

def sum_list(a, b):
    if len(a) == len(b):
        c = []
        for i in range(len(a)):
            c.append(a[i])
            c.append(b[i])
        return c
print(sum_list(a,b))