Generates a random string, consisting of upper and lower case letters (of the English alphabet),
        digits (0-9), and symbols ("_,.:-/.[].{},#-!,$=%.+^.&*-() ").

        :param min_size: (optional) minimum string length.

        :param max_size: maximum string length.

        :return: a random string.

def next_string(min_size, max_size):
        """
        Generates a random string, consisting of upper and lower case letters (of the English alphabet),
        digits (0-9), and symbols ("_,.:-/.[].{},#-!,$=%.+^.&*-() ").

        :param min_size: (optional) minimum string length.

        :param max_size: maximum string length.

        :return: a random string.
        """
        result = ''
        
        max_size = max_size if max_size != None else min_size
        length = RandomInteger.next_integer(min_size, max_size)
        for i in range(length):
            result += random.choice(_chars)

        return result