Python file merger

merger.py

import sys, hashlib, argparse

parser = argparse.ArgumentParser(description='Merge files.')
parser.add_argument('files', type=argparse.FileType('r'), nargs='+')

args = parser.parse_args()

output_file = "output"

def concat(files):
    with open(output_file, "ab") as out1:
        for f in files:
            with open(f.name, "rb") as fp:
                out1.write(fp.read())
                fp.close()
        out1.close
    print("merged into : " + output_file)
	
    with open(output_file, "rb") as f:
        md5 = hashlib.md5(f.read()).hexdigest()
	
    print("MD5 : " + md5)

concat(args.files)