Convert a string from one charset to another.

def change_charset(s, original_charset, target_charset):
    """ Convert a string from one charset to another.
    """
    if not isinstance(s, str):
        raise ValueError('"s" must be a string.')

    intermediate_integer = charset_to_int(s, original_charset)
    output_string = int_to_charset(intermediate_integer, target_charset)
    return output_string