class_docstr: Dynamically substituted for GroupBy.nth to enable both call and index
code: def __call__(
      self,
      n: PositionalIndexer | tuple,
      dropna: Literal["any", "all", None] = None,
  ) -> DataFrame | Series:
      return self.groupby_object._nth(n, dropna)
  
imports: from __future__ import annotations
  from collections.abc import Iterable
  from typing import TYPE_CHECKING, Literal, cast
  import numpy
  from pandas.util._decorators import cache_readonly, doc
  from pandas.core.dtypes.common import is_integer, is_list_like
label_desc: Use image node_id 2 for calling the GroupByNthSelector obj's underlying member method code with example usage: obj.__call__(n, dropna) and returns: self