code: def isin(self, values):
          
          if not isinstance(values, type(self)):
              try:
                  values = type(self)(values)
              except ValueError:
                  return self.astype(object).isin(values)
  
          return algorithms.isin(self.asi8, values.asi8)
docs: Compute boolean array of whether each index value is found in the
          passed set of values.
  
          Parameters
          ----------
          values : set or sequence of values
  
          Returns
          -------
          is_contained : ndarray (boolean dtype)