chore: add protocol

Author: d-v-b

src/zarr/storage/_utils.py

@@ -6,7 +6,7 @@
 import importlib
 import re
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, ParamSpec, TypeVar
+from typing import TYPE_CHECKING, Any, ParamSpec, Protocol, TypeVar
 
 from zarr.abc.store import OffsetByteRequest, RangeByteRequest, SuffixByteRequest
 
@@ -29,6 +29,12 @@ class UPath:  # type: ignore[no-redef]
 T_co = TypeVar("T_co", covariant=True)
 
 
+class HasConcurrencyLimit(Protocol):
+    """Protocol for objects that support semaphore-based concurrency limiting."""
+
+    def _limit(self) -> asyncio.Semaphore | contextlib.nullcontext[None]: ...
+
+
 class ConcurrencyLimiter:
     """Mixin that adds a semaphore-based concurrency limit to a store.
 
@@ -82,8 +88,8 @@ async def get(self, key, prototype, byte_range=None):
 
     @functools.wraps(func)
     async def wrapper(*args: P.args, **kwargs: P.kwargs) -> T_co:
-        self = args[0]
-        async with self._limit():  # type: ignore[attr-defined]
+        self: HasConcurrencyLimit = args[0]  # type: ignore[assignment]
+        async with self._limit():
             return await func(*args, **kwargs)
 
     return wrapper