def getPayments(stream_payment_file):
    """
        Open stream_payment_file and extract two user IDs from each payment.
        Store each payment as a tuple (userID1, userID2).
    """
    payments = []
    with open(stream_payment_file, "r") as f:
        f.readline() # skip the header
        for line in f:
            cell = line.strip().split(',')
            id1 = cell[1].strip()
            id2 = cell[2].strip()
            payments.append((id1, id2))
    return payments