Given two sorted lists, return a merged sorted list

merge.py

# Given two sorted lists A and B, return a sorted list that has all
# the elements of A and all the elements of B.
def merge(A, B):
    i, j = 0, 0
    result = []
    while True:
        if i == len(A):
            # Put the rest of B into result.
            while j < len(B):
                result.append(B[j])
                j += 1
            break
        elif j == len(B):
            # Put the rest of A into result.
            while i < len(A):
                result.append(A[i])
                i += 1
            break
        elif A[i] <= B[j]:
            # Put the A element into result and increase i.
            result.append(A[i])
            i += 1
        else:
            # Put the B element into result and increase j.
            result.append(B[j])
            j += 1
    # We're out of the loop now, so we can return the result.
    return result


assert merge([], []) == []
assert merge([4], []) == [4]
assert merge([], [4]) == [4]
assert merge([3], [7]) == [3,7]
assert merge([7], [3]) == [3,7]
A = [3,5,6,9]
B = [1,2,5,7,9]
assert merge(A,B) == [1,2,3,5,5,6,7,9,9]
print("All tests passed.")