code: def predict_median(self, X, ancillary_X=None):
          
          exp_mu_, _ = self._prep_inputs_for_prediction_and_return_scores(X, ancillary_X)
          return pd.DataFrame(exp_mu_, index=_get_index(X))
docs: Returns the median lifetimes for the individuals. If the survival curve of an
          individual does not cross 0.5, then the result is infinity.
          http://stats.stackexchange.com/questions/102986/percentile-loss-functions
  
          Parameters
          ----------
          X:  numpy array or DataFrame
              a (n,d) covariate numpy array or DataFrame. If a DataFrame, columns
              can be in any order. If a numpy array, columns must be in the
              same order as the training data.
          ancillary_X: numpy array or DataFrame, optional
              a (n,d) covariate numpy array or DataFrame. If a DataFrame, columns
              can be in any order. If a numpy array, columns must be in the
              same order as the training data.
          p: float, optional (default=0.5)
              the percentile, must be between 0 and 1.
  
          Returns
          -------
          DataFrame
  
          See Also
          --------
          predict_percentile