|---| | [ View source on GitHub](https://github.com/tensorflow/agents/blob/v0.19.0/tf_agents/utils/nest_utils.py#L195-L311) | Recursively prunes keys from `wide` if they don't appear in `narrow`. tf_agents.utils.nest_utils.prune_extra_keys( narrow, wide ) Often used as preprocessing prior to calling [`tf.nest.flatten`](https://www.tensorflow.org/api_docs/python/tf/nest/flatten) or [`tf.nest.map_structure`](https://www.tensorflow.org/api_docs/python/tf/nest/map_structure). This function is more forgiving than the ones in `nest`; if two substructures' types or structures don't agree, we consider it invalid and `prune_extra_keys` will return the `wide` substructure as is. Typically, additional checking is needed: you will also want to use `nest.assert_same_structure(narrow, prune_extra_keys(narrow, wide))` to ensure the result of pruning is still a correct structure. #### Examples: wide = [{"a": "a", "b": "b"}] # Narrows 'wide' assert prune_extra_keys([{"a": 1}], wide) == [{"a": "a"}] # 'wide' lacks "c", is considered invalid. assert prune_extra_keys([{"c": 1}], wide) == wide # 'wide' contains a different type from 'narrow', is considered invalid assert prune_extra_keys("scalar", wide) == wide # 'wide' substructure for key "d" does not match the one in 'narrow' and # therefore is returned unmodified. assert (prune_extra_keys({"a": {"b": 1}, "d": None}, {"a": {"b": "b", "c": "c"}, "d": [1, 2]}) == {"a": {"b": "b"}, "d": [1, 2]}) # assert prune_extra_keys((), wide) == () # assert prune_extra_keys({"a": ()}, wide) == {"a": ()}


| ## Args || |---|---| | `narrow` | A nested structure. | | `wide` | A nested structure that may contain dicts with more fields than `narrow`. |



| ## Returns || |---|---| | A structure with the same nested substructures as `wide`, but with dicts whose entries are limited to the keys found in the associated substructures of `narrow`.
In case of substructure or size mismatches, the returned substructures will be returned as is. Note that ObjectProxy-wrapped objects are considered equivalent to their non-ObjectProxy types. ||