Union of two sorted sequences (A and B aren't empty)

union.py

def union(A, i, B, j, C):
    if (i >= len(A)) and (j >= len(B)) and (max(A[-1], B[-1]) == C[-1]):
        return C

    if (i == len(A)) and (j <= len(B)) and (C[-1] < B[j]):
        C.append(B[j])
        return union(A, i, B, j + 1, C)

    if (j == len(B)) and (i <= len(A)) and (C[-1] < A[i]):
        C.append(A[i])
        return union(A, i + 1, B, j, C)

    if A[i] < B[j]:
        C.append(A[i])
        return union(A, i + 1, B, j, C)
    elif A[i] == B[j]:
        C.append(A[i])
        return union(A, i + 1, B, j + 1, C)
    else:
        C.append(B[j])
        return union(A, i, B, j + 1, C)

if __name__ == '__main__':
    L1 = [2, 3, 5]
    L2 = [1, 3, 5, 7]

    print union(L2, 0, L1, 0, [])