class_docstr: Groups an Element pair such that we have (ElementX, List[ElementY]).
code: def keys(self) -> List[ElementX]:  # noqa :D
      return list(self._groups.keys())
  
file_path: metricflow/metricflow/model/semantics/element_group.py
imports: from __future__ import annotations
  import collections
  from typing import Dict, Generic, List, TypeVar
label_desc: Use image node_id 4 for calling the ElementGrouper obj's underlying member method code with example usage: obj.keys() and returns: list