Merge sort implementing true external sequential file/stream emulation

merge_sort_bingo.py

def read_chunk(dst, src, chunk_size, pos, len_src):
    while chunk_size > 0 and pos < len_src:
        dst.append(src[pos])
        pos += 1
        chunk_size -= 1
    return pos

def get_bingo_size(pos, chunk_size, len_src):
    if pos + chunk_size > len_src:
        return len_src - pos
    return chunk_size

input = (9,0,7,8,3,11,1,5,0,5,10)
len_input = len(input)
chunk_size = 1
va = None
vb = None

while chunk_size < len_input:
    a = []
    b = []
    pos = 0

    while pos < len_input:
        pos = read_chunk(a, input, chunk_size, pos, len_input)
        pos = read_chunk(b, input, chunk_size, pos, len_input)

    pos_a = 0
    pos_b = 0
    len_a = len(a)
    len_b = len(b)
    input = []

    while True:
        bingo_a = get_bingo_size(pos_a, chunk_size, len_a)
        bingo_b = get_bingo_size(pos_b, chunk_size, len_b)

        if bingo_a + bingo_b == 0:
            break

        read_a = bingo_a > 0
        read_b = bingo_b > 0
        write_a = False
        write_b = False

        while True:
            if read_a:
                va = a[pos_a]
                pos_a += 1
                write_a = True

            if read_b:
                vb = b[pos_b]
                pos_b += 1
                write_b = True

            if write_a and write_b:
                if va < vb:
                    read_b = write_b
                    write_b = False
                else:
                    read_a = write_a
                    write_a = False

            if write_a:
                input.append(va)
                write_a = False
                bingo_a -= 1
                read_a = bingo_a > 0
                write_b = read_b
                read_b = False
            elif write_b:
                input.append(vb)
                write_b = False
                bingo_b -= 1
                read_b = bingo_b > 0
                write_a = read_a
                read_a = False
            else:
                break

    chunk_size *= 2

print(input)