def __init__(self,
               example_to_crowding_key: Callable[[Example], str],
               max_per_crowding_key: int = 1):
    """Initializes the CrowdedNeighborFilter.

    Args:
      example_to_crowding_key: A function mapping Example to a crowding key.
      max_per_crowding_key: Maximum number of neighbors per crowding key.
    """
    self._example_to_crowding_key = example_to_crowding_key
    self._max_per_crowding_key = max_per_crowding_key
Initializes the CrowdedNeighborFilter.

    Args:
      example_to_crowding_key: A function mapping Example to a crowding key.
      max_per_crowding_key: Maximum number of neighbors per crowding key.
    
language/casper/retrieve/query_retrievers.py