py-regex-replace/src/py_regex_replace/main.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import argparse
import re
import sys


def main():
    pattern, repl, string, count = parse_args()

    # https://docs.python.org/3/library/re.html#re.MULTILINE
    # re.MULTILINE
    # When specified, the pattern character '^' matches at the beginning of the string
    # and at the beginning of each line (immediately following each newline);
    # and the pattern character '$' matches at the end of the string
    # and at the end of each line (immediately preceding each newline).

    # https://docs.python.org/3/library/re.html#re.findall
    # Return all non-overlapping matches of pattern in string, as a list of strings or tuples.
    # The string is scanned left-to-right, and matches are returned in the order found.
    matches = re.findall(pattern, string, flags=re.MULTILINE)
    if len(matches) != count:
        print(f'[ERROR] Expected {count} matches of pattern in string, but got {len(matches)}.')
        exit(1)

    # https://docs.python.org/3/library/re.html#re.sub
    # Return the string obtained by replacing the leftmost non-overlapping occurrences of `pattern`
    # in `string` by the replacement `repl`.
    string = re.sub(pattern, repl, string, flags=re.MULTILINE)

    print(string, end='')


def parse_args():
    parser = argparse.ArgumentParser(prog='py-regex-replace')

    parser.add_argument('--pattern', '-p',
                        help='regex search pattern',
                        required=True, type=str)
    parser.add_argument('--repl', '-r',
                        help='replacement',
                        required=True, type=str)
    parser.add_argument('--count', '-c',
                        help='expected count of pattern in string',
                        default=1, type=int)

    args = parser.parse_args()

    string = sys.stdin.read()
    if len(string) == 0:
        print('[WARNING] The given string is empty.', file=sys.stderr)

    return args.pattern, args.repl, string, args.count


if __name__ == '__main__':
    main()