code: def load_variants(self, patients=None, filter_fn=None, **kwargs):
          
          filter_fn = first_not_none_param([filter_fn, self.filter_fn], no_filter)
          filter_fn_name = self._get_function_name(filter_fn)
          logger.debug("loading variants with filter_fn: {}".format(filter_fn_name))
          patient_variants = {}
  
          for patient in self.iter_patients(patients):
              variants = self._load_single_patient_variants(patient, filter_fn, **kwargs)
              if variants is not None:
                  patient_variants[patient.id] = variants
          return patient_variants
docs: Load a dictionary of patient_id to varcode.VariantCollection
  
          Parameters
          ----------
          patients : str, optional
              Filter to a subset of patients
          filter_fn : function
              Takes a FilterableVariant and returns a boolean. Only variants returning True are preserved.
              Overrides default self.filter_fn. `None` passes through to self.filter_fn.
  
          Returns
          -------
          merged_variants
              Dictionary of patient_id to VariantCollection