def _parse_src(cls, src_contents, src_filename):
        """
        Return a stream of `(token_type, value)` tuples
        parsed from `src_contents` (str)

        Uses `src_filename` to guess the type of file
        so it can highlight syntax correctly.
        """

        # Parse the source into tokens
        try:
            lexer = guess_lexer_for_filename(src_filename, src_contents)
        except ClassNotFound:
            lexer = TextLexer()

        # Ensure that we don't strip newlines from
        # the source file when lexing.
        lexer.stripnl = False

        return pygments.lex(src_contents, lexer)