code: def _tokenize(self, source, name, filename=None, state=None):
          
          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
docs: Called by the parser to do the preprocessing and filtering
          for all the extensions.  Returns a :class:`~jinja2.lexer.TokenStream`.