text: from .base import BaseSelector
  import numpy as np
  from .. import register_feature
  
  
  @register_feature("SeFilterConstant")
  class SeFilterConstant(BaseSelector):
      r"""drop constant features"""
  
      def _fit(self, data):
          d1, d2 = data.x.shape
          xx = data.x
          # if d2>=d1:
          #     if np.allclose(xx[:,:d1],np.eye(d1)):
          #         return np.empty((d1,0))
          self._sel = np.where(np.all(xx == xx[0, :], axis=0) == False)[0]
  