code: def triggering_streams(streams):
      
      for stream in streams:
          stream._triggering = True
      try:
          yield
      except:
          raise
      finally:
          for stream in streams:
              stream._triggering = False
docs: Temporarily declares the streams as being in a triggered state.
      Needed by DynamicMap to determine whether to memoize on a Callable,
      i.e. if a stream has memoization disabled and is in triggered state
      Callable should disable lookup in the memoization cache. This is
      done by the dynamicmap_memoization context manager.