input: def replace_all_occurrences(str: str, char: str, replacement: str) -> str:
      """ Replace all occurrences of a given character in a string with the provided
      replacement character.
      
      >>> replace_all_occurrences("Hello World!", 'l', 'X')
      'HeXXo WorXd!'
      >>> replace_all_occurrences("Python is fun!", 'n', 'z')
      'Pythoz is fuz!'
      """
output:     return str.replace(char, replacement)