docs: def _lazy_turbo_mapping(initial, pre_size):
      '''
      _lazy_turbo_mapping is a blatant copy of the pyrsistent._pmap._turbo_mapping function, except
      it works for lazy maps; this seems like the only way to fully overload PMap.
      '''
      size = pre_size or (2 * len(initial)) or 8
      buckets = size * [None]
      if not isinstance(initial, colls.Mapping): initial = dict(initial)
      for k, v in six.iteritems(initial):
          h = hash(k)
          index = h % size
          bucket = buckets[index]
          if bucket: bucket.append((k, v))
          else:      buckets[index] = [(k, v)]
      return LazyPMap(len(initial), ps.pvector().extend(buckets))