python program to open all files in a directory and concatenate their contents into a single output file

concatenate.py

from glob import iglob
import shutil
import os
import fileinput
PATH = '*.csv'
with open("all_da.txt", 'w') as fout:
    for filename in iglob(PATH):
        for line in fileinput.input(filename):
            fout.write(line)