code: def lf_polarities(L):
      
      polarities = [sorted(list(set(L[:, i].data))) for i in range(L.shape[1])]
      return [p[0] if len(p) == 1 else p for p in polarities]
docs: Return the polarities of each LF based on evidence in a label matrix.
  
      Args:
          L: an n x m scipy.sparse matrix where L_{i,j} is the label given by the
              jth LF to the ith candidate