Clarify ChunkKeyEncoding base class

- Enforce encode_chunk_key to be implemented (abstractmethod in ABC)
- Make decode_chunk_key optional (raise NotImplementedError by default)
Note, the latter is never raised by the current zarr implementation.

Author: RFLeijenaar

src/zarr/core/chunk_key_encodings.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from abc import abstractmethod
+from abc import ABC, abstractmethod
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Literal, TypeAlias, TypedDict, cast
 
@@ -29,7 +29,7 @@ class ChunkKeyEncodingParams(TypedDict):
 
 
 @dataclass(frozen=True)
-class ChunkKeyEncoding(Metadata):
+class ChunkKeyEncoding(ABC, Metadata):
     name: str
     separator: SeparatorLiteral = "."
 
@@ -45,13 +45,19 @@ def from_dict(cls, data: dict[str, JSON]) -> Self:
     def to_dict(self) -> dict[str, JSON]:
         return {"name": self.name, "configuration": {"separator": self.separator}}
 
-    @abstractmethod
     def decode_chunk_key(self, chunk_key: str) -> tuple[int, ...]:
-        pass
+        """
+        Optional: decode a chunk key string into chunk coordinates.
+        Not required for normal operation; override if needed for testing or debugging.
+        """
+        raise NotImplementedError(f"{self.__class__.__name__} does not implement decode_chunk_key.")
 
     @abstractmethod
     def encode_chunk_key(self, chunk_coords: tuple[int, ...]) -> str:
-        pass
+        """
+        Encode chunk coordinates into a chunk key string.
+        Must be implemented by subclasses.
+        """
 
 
 ChunkKeyEncodingLike: TypeAlias = dict[str, JSON] | ChunkKeyEncodingParams | ChunkKeyEncoding

src/zarr/registry.py

@@ -65,7 +65,6 @@ def register(self, cls: type[T], qualname: str | None = None) -> None:
 __ndbuffer_registry: Registry[NDBuffer] = Registry()
 __chunk_key_encoding_registry: Registry[ChunkKeyEncoding] = Registry()
 
-# CHANGE: Consider updating docstring
 """
 The registry module is responsible for managing implementations of codecs,
 pipelines, buffers, ndbuffers, and chunk key encodings and collecting them from entrypoints.