class_docstr: IsInf Operator
  
  Parameters
  ----------
  feature : Expression
      feature instance
  
  Returns
  ----------
  feature:
      A series indicating whether the feature is inf
class_docstr_tok: ["IsInf","Operator","Parameters","--","--","--","--","--","feature",":","Expression","feature","instance","Returns","--","--","--","--","--","feature",":","A","series","indicating","whether","the","feature","is","inf"]
code: def _load_internal(self, instrument, start_index, end_index, freq):
      series = self.feature.load(
          instrument, start_index, end_index, freq
      )
      return np.isinf(series)
  
imports: import numpy
  import pandas
  from datetime import datetime
  from qlib.data.cache import H
  from qlib.data.data import Cal
  from qlib.data.ops import ElemOperator, PairOperator
  from qlib.utils.time import time_to_day_index
label_desc: Use image node_id 1 for calling the IsInf obj's underlying member method code with example usage: obj._load_internal(instrument, start_index, end_index, freq) and returns: np