code: def push_source(self, newstream, newfile=None):
          "Push an input source onto the lexer's input source stack."
          if isinstance(newstream, basestring):
              newstream = StringIO(newstream)
          self.filestack.appendleft((self.infile, self.instream, self.lineno))
          self.infile = newfile
          self.instream = newstream
          self.lineno = f push_source(self, newstream, newfile=None):
          "Push an input source onto the lexer's input source stack."
          if isinstance(newstream, basestring):
              newstream = StringIO(newstream)
          self.filestack.appendleft((self.infile, self.instream, self.lineno))
          self.infile = newfile
          self.instream = newstream
          self.lineno = 1
docs: Push an input source onto the lexer's input source stack.