code: def dangling(self):
          
          if len(self.paths) == 0:
              return np.arange(len(self.entities))
          else:
              included = np.hstack(self.paths)
          dangling = np.setdiff1d(np.arange(len(self.entities)),
                                  included)
          return dangling
docs: List of entities that aren't included in a closed path
  
          Returns
          ----------
          dangling: (n,) int, index of self.entities