code: def pop_source(self):
          "Pop the input source stack."
          self.instream.close()
          (self.infile, self.instream, self.lineno) = self.filestack.popleft()
          self.state = ' f pop_source(self):
          "Pop the input source stack."
          self.instream.close()
          (self.infile, self.instream, self.lineno) = self.filestack.popleft()
          self.state = ' '
docs: Pop the input source stack.