Allow to deserialize an example even if a key exists that wasn't found in the specs.

This matches tf.data's path:

```python
import numpy as np
import tensorflow_datasets as tfds

required_feature = tfds.features.FeaturesDict({
    'required': tfds.features.Scalar(dtype=np.str_)
})

optional_feature = tfds.features.FeaturesDict({
    'optional': tfds.features.Scalar(dtype=np.str_, optional=True)
})

serialized_element = required_feature.serialize_example({'required': 'hello world'})
optional_feature.deserialize_example(serialized_element)
```
PiperOrigin-RevId: 690987105

Author: marcenacp

tensorflow_datasets/core/example_parser.py

@@ -154,7 +154,6 @@ def _features_to_numpy(
   parsed_example = {}
   feature_map = features.feature
   for key in feature_map:
-    ragged_row_length = _RAGGED_ROW_LENGTH_REGEX.match(key)
     ragged_flat_values = _RAGGED_FLAT_VALUES_REGEX.match(key)
     # For ragged arrays we need to reshape the np.arrays using
     # ragged_flat_values/ragged_row_lengths_*. `features` can look like:
@@ -173,14 +172,13 @@ def _features_to_numpy(
             flat_example_specs[feature_name],
             key,
         )
-    elif ragged_row_length:
-      # Lengths are extracted later for each feature in _feature_to_numpy.
-      continue
     else:
-      raise KeyError(
-          f"Malformed input: {key} is found in the feature, but not in"
-          f" {flat_example_specs}"
-      )
+      # Possible cases when we land here:
+      # 1. Case ragged: Lengths are extracted later for each feature in
+      #    _feature_to_numpy. So we continue.
+      # 2. Other case: a key was found in the feature, but not in the specs. We
+      #    just ignore this feature and continue.
+      continue
   return parsed_example
 
 

tensorflow_datasets/core/example_parser_test.py

@@ -116,11 +116,8 @@ def test_key_error_exception_if_example_specs_is_malformed():
   ).SerializeToString()
   example_specs = features.get_tensor_info()
   example_parser_np = example_parser.ExampleParserNp(example_specs)
-  with pytest.raises(
-      KeyError,
-      match='(.|\n)*array_of_ints is found in the feature, but not in*',
-  ):
-    example_parser_np.parse_example(serialized_example)
+  deserialized_example = example_parser_np.parse_example(serialized_example)
+  np.testing.assert_equal(deserialized_example, {'doesnotexist': None})
 
 
 @pytest.mark.parametrize(