def pystr(
        self,
        min_chars: Optional[int] = None,
        max_chars: int = 20,
        prefix: str = "",
        suffix: str = "",
    ) -> str:
        """
        Generates a random string of upper and lowercase letters.

        :param min_chars: minimum length of the random part.
        :param max_chars: maximum length of the random part.
        :param prefix: an optional prefix to prepend to the random string.
        :param suffix: an optional suffix to append to the random string.
        :return: Random of random length between min and max characters.
        """
        if min_chars is None:
            chars = "".join(self.random_letters(length=max_chars))
        else:
            assert max_chars >= min_chars, "Maximum length must be greater than or equal to minimum length"
            chars = "".join(
                self.random_letters(
                    length=self.generator.random.randint(min_chars, max_chars),
                ),
            )

        return prefix + chars + suffix

        Generates a random string of upper and lowercase letters.

        :param min_chars: minimum length of the random part.
        :param max_chars: maximum length of the random part.
        :param prefix: an optional prefix to prepend to the random string.
        :param suffix: an optional suffix to append to the random string.
        :return: Random of random length between min and max characters.
        
faker/providers/python/__init__.py