support for custom feature encoding/decoding (#7284)

* support for custom feature encoding/decoding

* Update src/datasets/features/features.py

---------

Co-authored-by: Quentin Lhoest <[email protected]>

Author: alex-hh

src/datasets/features/features.py

@@ -1348,7 +1348,7 @@ def encode_nested_example(schema, obj, level=0):
             return list(obj)
     # Object with special encoding:
     # ClassLabel will convert from string to int, TranslationVariableLanguages does some checks
-    elif isinstance(schema, (Audio, Image, ClassLabel, TranslationVariableLanguages, Value, _ArrayXD, Video)):
+    elif hasattr(schema, "encode_example"):
         return schema.encode_example(obj) if obj is not None else None
     # Other object should be directly convertible to a native Arrow type (like Translation and Translation)
     return obj
@@ -1399,10 +1399,9 @@ def decode_nested_example(schema, obj, token_per_repo_id: Optional[Dict[str, Uni
         else:
             return decode_nested_example([schema.feature], obj)
     # Object with special decoding:
-    elif isinstance(schema, (Audio, Image, Video)):
+    elif hasattr(schema, "decode_example") and getattr(schema, "decode", True):
         # we pass the token to read and decode files from private repositories in streaming mode
-        if obj is not None and schema.decode:
-            return schema.decode_example(obj, token_per_repo_id=token_per_repo_id)
+        return schema.decode_example(obj, token_per_repo_id=token_per_repo_id) if obj is not None else None
     return obj
 
 
@@ -1629,7 +1628,9 @@ def require_decoding(feature: FeatureType, ignore_decode_attribute: bool = False
     elif isinstance(feature, Sequence):
         return require_decoding(feature.feature)
     else:
-        return hasattr(feature, "decode_example") and (feature.decode if not ignore_decode_attribute else True)
+        return hasattr(feature, "decode_example") and (
+            getattr(feature, "decode", True) if not ignore_decode_attribute else True
+        )
 
 
 def require_storage_cast(feature: FeatureType) -> bool: