pmch.py

#!/usr/bin/env python3
from sys import argv
from math import factorial


def parse_fasta(in_file):
    """ return sequence from single fasta """
    seqs = [line for line in open(in_file) if not line.startswith(">")]
    return "".join(seqs).replace("\n", "")


def pmch(seq):
    """ return number of perfect matchings of basepair edges in sequence """
    return factorial(seq.count("A")) * factorial(seq.count("C"))


def main(fasta_path):
    sequence = parse_fasta(fasta_path)
    return pmch(sequence)


if __name__ == "__main__":
    print(main(argv[1]))