Checks for the validity of numbers following the Luhn algorithm

luhn_checker.py

#!/usr/bin/env python3
"""
Checks for the validity of numbers following the Luhn algorithm

Samuel Prevost 2021-04-01
"""

import os
import sys
import numpy as np
import argparse


def main():
    """Main function"""
    main_arg_parser = argparse.ArgumentParser(
        description="Checks for the validity of numbers following the Luhn algorithm"
    )
    main_arg_parser.add_argument(
        "-i",
        "--input",
        required=False,
        help="Path to a file containing the numbers, or directly the number itself."
        "If not provided, or - provided, reads from stdin.",
    )
    main_arg_parser.add_argument(
        "-q",
        "--quick",
        action="store_true",
        help="Quickly quits as soon as an invalid number is found, if any",
    )
    main_arg_parser.add_argument(
        "--csv",
        action="store_true",
        help="Prints a CSV file to stdout containing the bad numbers founds",
    )
    main_arg_parser.add_argument(
        "-v",
        "--verbose",
        action="store_true",
        help="Displays helpful information along",
    )

    args = main_arg_parser.parse_args()

    # Flag that will get updated as we go along
    all_good = True

    if args.csv:
        print("Incorrect Numbers")

    if args.input is not None and args.input != "-" and not os.path.isfile(args.input):
        args.input = "".join([a for a in args.input if a.replace(" ", "").isnumeric()])

        valid = check_numbers([args.input], out_csv=args.csv, verbose=args.verbose)

        if valid:
            if args.verbose:
                print("Valid number", file=sys.stderr)
            sys.exit(0)
        else:
            if args.verbose:
                print("Invalid number", file=sys.stderr)
            sys.exit(1)
    else:
        iterator = None

        if args.input is None or args.input == "-":
            iterator = iter(sys.stdin)
        elif os.path.isfile(args.input):
            f = open(args.input, "r")
            iterator = iter(f)
        else:
            print(f"Invalid argument for --input: {args.input}")
            sys.exit(1)

        try:
            buffer_size = 3000
            lines = []

            for i, line in enumerate(iterator):
                if len(lines) < buffer_size:
                    line = line.replace("\n", "")

                    if len(line) == 0:
                        continue
                    lines.append(line)
                else:
                    all_good &= check_numbers(
                        lines, out_csv=args.csv, verbose=args.verbose
                    )
                    lines = []

                    if args.quick and not all_good:
                        if args.verbose:
                            print(
                                f"Some numbers were invalid before line {i+1}",
                                file=sys.stderr,
                            )
                        break

            if len(lines) > 0:
                all_good &= check_numbers(lines, out_csv=args.csv, verbose=args.verbose)
                lines = []

            if all_good and args.verbose:
                print("All number were valid", file=sys.stderr)

        except KeyboardInterrupt:
            sys.stdout.flush()

        finally:
            if hasattr(iterator, "close") and callable(iterator.close):
                iterator.close()

    if args.verbose:
        print("Done.", file=sys.stderr)

    # True ==> 1 ==> error exit code
    # False ==> 0 ==> all good exit code
    # hence the inversion
    sys.exit(int(not all_good))


def check_numbers(numbers, out_csv=False, verbose=False):
    digits = []

    for num in numbers:
        digits.append([int(c) for c in num])
    arr = np.array(digits, dtype=np.uint64)
    # Double every other digit starting from the last, excluded
    arr[:, :-1:2] *= 2
    # then remove 9 where it's more than one digit
    # (equiv to add the two digits if over ten)
    arr[:, :-1:2][arr[:, :-1:2] > 9] -= 9
    result = np.mod(arr.sum(axis=1), 10) == 0

    all_valid = np.all(result)
    if not all_valid and (verbose or out_csv):
        bad = [num for good, num in zip(result, numbers) if not good]
        print("\n".join(bad))

    return all_valid


if __name__ == "__main__":
    main()