code: def push(self, stream, value):
          
  
          if not self.matches(stream):
              raise ArgumentError("Attempting to push reading to stream walker that does not match", selector=self.selector, stream=stream)
  
          self.reading = value
docs: Update this stream walker with a new responsive reading.
  
          Virtual stream walkers keep at most one reading so this function
          just overwrites whatever was previously stored.