code: def filter_players(self, pl_filter):
          
          def each(d):
              return {
                  k: v
                  for k, v in d.items()
                  if pl_filter(k, v)
              }
              
          return self.__apply_to_both(each)
docs: Return the subset home and away players that satisfy the provided filter function.
          
          :param pl_filter: function that takes a by player dictionary and returns bool
          :returns: dict of the form ``{ 'home/away': { by_player_dict } }``. See :py:func:`home_players` and :py:func:`away_players`