from pathlib import Path
from collections import defaultdict

mapping = defaultdict(int)

with Path("chatmgs212.txt").open("rb") as file:
    for line in file:
        mapping[line.strip()] += 1

with Path("how_manymgs21.txt").open("wb") as file:
    vals = sorted([(v,k) for k,v in mapping.items()],reverse=True)
    file.writelines([f"{n} - {v}: {k.decode()}\n".encode() for n,(v,k) in enumerate(vals,start=1)])