Yet another password generator

genpass.py

#!/usr/bin/env python3
# vim:fenc=utf-8
#
# Copyright © 2026 fred <github-fred@hidzz.com>
#
# Distributed under terms of the BSD 3-Clause license.

import os
import secrets
import sys
from functools import lru_cache
from pathlib import Path
from typing import List

DICT_FILE = Path('/usr/share/dict/words')

# Most common word with a length of 3 to 6 characters.
# https://gist.github.com/deekayen/4148741
COMMON_WORDS = [
  "that", "have", "with", "this", "from", "they", "will", "would", "there",
  "their", "what", "about", "which", "when", "make", "like", "time", "just",
  "know", "take", "people", "into", "year", "your", "good", "some", "could",
  "them", "other", "than", "then", "look", "only", "come", "over", "think",
  "also", "back", "after", "work", "first", "well", "even", "want", "these",
  "give", "most",
]

# Secure random for shuffling
_RANDOM = secrets.SystemRandom()


@lru_cache(maxsize=1)
def all_words() -> List[str]:
  words = set()
  if not DICT_FILE.exists():
    print(f'The dictionnary file "{DICT_FILE}" does not exists')
    sys.exit(os.EX_OSFILE)

  with DICT_FILE.open('r', encoding='utf-8', errors='replace') as fd:
    for word in fd:
      word = word.strip().lower()
      if word in COMMON_WORDS:
        continue
      # Remove words with accents because they might be challenging to type
      # with some keyboards.
      if "'" in word or not word.isascii():
        continue
      if 3 < len(word) < 6:
        words.add(word)
  print(f'=== {len(words)} selected ===')
  return list(words)


def _maybe_transform(word: str) -> str:
  """Optionally transform a word with leetspeak substitutions."""
  # Use a consistent mapping
  leet_map = {'i': '!', 'e': '3', 'o': '0', 'a': '@', 's': '$'}

  # Transform 40% of transformable characters
  transformed = []
  chances = 50
  for char in word:
    if char in leet_map and secrets.randbelow(100) < chances:
      transformed.append(leet_map[char])
      chances = chances - 5 if chances > 0 else chances
    else:
      transformed.append(char)
  return ''.join(transformed)


def make_password(length: int = 4, leet_chance: float = 0.4) -> str:
  if length < 1:
    raise ValueError('Length must be at least 1')

  words = all_words()
  if not words:
    raise RuntimeError('No words available for password generation')

  password = [secrets.choice(words) for _ in range(length)]

  # Apply leetspeak substitution to random words
  for i in range(length):
    if secrets.randbelow(100) < leet_chance * 100:
      password[i] = _maybe_transform(password[i])

  _RANDOM.shuffle(password)
  return '-'.join(password)


def main():
  for _ in range(6):
    password = make_password(4)
    print(f'{len(password)} = {password}')


if __name__ == "__main__":
  main()

#