calculate combinatorial problems

main.py

# This is a sample Python script.
# You can use it to calculate combinatorial problems
# magicwenli on 2021.09.23

import argparse
import math
from fractions import Fraction


def combA(arguments: list):
    sums = 0
    for i in range(len(arguments) // 2):
        a = arguments[i]
        b = arguments[i + 1]
        if a < b:  # a是底数
            a, b = b, a
        sums += math.comb(a, b)
    return sums


def main():
    # Create the parser
    my_parser = argparse.ArgumentParser(description='Calculate combs',
                                        epilog="Try: python main.py 8 2 5 2 -d 13 2. And you may get 19/39.")

    # Add the arguments
    my_parser.add_argument('up',
                           nargs='+',
                           type=int,
                           help='upper part of fraction, use a list like `3 1 2 1`')

    my_parser.add_argument('-d',
                           '--down',
                           nargs='+',
                           type=int,
                           help='lower part of fraction, same as up')
    # Execute parse_args()
    args = my_parser.parse_args()

    print(f"ups: {args.up}\ndowns: {args.down}\n")

    ups = combA(args.up)
    downs = 0

    if args.down is None:
        print(ups)
        return ups
    else:
        downs = combA(args.down)

        print(f"{ups}/{downs} =")
        print(Fraction(ups, downs))
        return Fraction(ups, downs)


if __name__ == '__main__':
    main()