use local imports in store ABC to avoid circular import issues (#3372)

* use local imports in store ABC to avoid circular import issues

* changelog

Author: d-v-b

changes/3372.misc.rst

@@ -0,0 +1,2 @@
+Make certain imports in ``zarr.abc.store`` local to method definitions. This minimizes the risk of
+circular imports when adding new classes to ``zarr.abc.store``.

src/zarr/abc/store.py

@@ -6,10 +6,6 @@
 from itertools import starmap
 from typing import TYPE_CHECKING, Protocol, runtime_checkable
 
-from zarr.core.buffer.core import default_buffer_prototype
-from zarr.core.common import concurrent_map
-from zarr.core.config import config
-
 if TYPE_CHECKING:
     from collections.abc import AsyncGenerator, AsyncIterator, Iterable
     from types import TracebackType
@@ -438,6 +434,9 @@ async def getsize(self, key: str) -> int:
         # Note to implementers: this default implementation is very inefficient since
         # it requires reading the entire object. Many systems will have ways to get the
         # size of an object without reading it.
+        # avoid circular import
+        from zarr.core.buffer.core import default_buffer_prototype
+
         value = await self.get(key, prototype=default_buffer_prototype())
         if value is None:
             raise FileNotFoundError(key)
@@ -476,6 +475,11 @@ async def getsize_prefix(self, prefix: str) -> int:
         # on to getting sizes. Ideally we would overlap those two, which should
         # improve tail latency and might reduce memory pressure (since not all keys
         # would be in memory at once).
+
+        # avoid circular import
+        from zarr.core.common import concurrent_map
+        from zarr.core.config import config
+
         keys = [(x,) async for x in self.list_prefix(prefix)]
         limit = config.get("async.concurrency")
         sizes = await concurrent_map(keys, self.getsize, limit=limit)