code: def _prepare_window(self, start_time: datetime) -> None:
          
          # evaluate window first which sets the correct window in the store
          store = self._schema.schema_loader.get_store(
              self._schema.source.store_schema.fully_qualified_name)
          if Type.is_type_equal(self._schema.window_type, Type.DAY) or Type.is_type_equal(
                  self._schema.window_type, Type.HOUR):
              block_list = self._load_blocks(
                  store.get_range(
                      Key(self._schema.source.key_type, self._identity, self._schema.source.name),
                      start_time, self._get_end_time(start_time)))
          else:
              block_list = self._load_blocks(
                  store.get_range(
                      Key(self._schema.source.key_type, self._identity, self._schema.source.name),
                      start_time, None, self._schema.window_value))
  
          self._window_source = _WindowSource(block_list)
          self._validate_view()
docs: Prepares window if any is specified.
          :param start_time: The anchor block start_time from where the window
          should be generated.