Compare files line by line like linux command comm

compare_files_lines.py

import argparse

if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument("-a", "--action", dest="action", required=True,
                        choices=["inter", "union", "diff", "sydiff", "rdiff"])
    parser.add_argument(
        "A", type=argparse.FileType("r"), help="the base file")
    parser.add_argument(
        "B", type=argparse.FileType("r")
    )
    args = parser.parse_args()
    S = lambda f: set([line.strip() for line in f.readlines()])
    O = {"inter": set.__and__, "union": set.__or__, "diff": set.__sub__, "sydiff": set.__xor__,
         "rdiff": set.__rsub__}.get(args.action)(S(args.A), S(args.B))
    args.A.close()
    args.B.close()
    for i in O:
        print(i, flush=True)