Called by the parser to do the preprocessing and filtering
        for all the extensions.  Returns a :class:`~jinja2.lexer.TokenStream`.

def _tokenize(self, source, name, filename=None, state=None):
        """Called by the parser to do the preprocessing and filtering
        for all the extensions.  Returns a :class:`~jinja2.lexer.TokenStream`.
        """
        source = self.preprocess(source, name, filename)
        stream = self.lexer.tokenize(source, name, filename, state)
        for ext in self.iter_extensions():
            stream = ext.filter_stream(stream)
            if not isinstance(stream, TokenStream):
                stream = TokenStream(stream, name, filename)
        return stream