Function for calculatin hash

hash.py

import hashlib, sys, os


def calculate_hash(args):
    BUF_SIZE = 65536
    file_name = args[0]
    if not os.path.isfile(file_name):
        return "Not a file"

    sha1 = hashlib.sha1()
    with open(file_name, 'rb') as f:
        while True:
            data = f.read(BUF_SIZE)
            if not data:
                break
            sha1.update(data)

    return sha1.hexdigest()


if __name__ == "__main__":
    hsh = calculate_hash(sys.argv[1:])
    print(hsh)