From e492be23f8c36095a29902953e19a0892dd65c89 Mon Sep 17 00:00:00 2001
From: Davis Bennett <davis.v.bennett@gmail.com>
Date: Tue, 26 Mar 2024 21:04:57 +0100
Subject: [PATCH] feat: functional .children method for groups

---
 src/zarr/v3/group.py   | 37 ++++++++++++++++++++++++++++++++++---
 tests/test_group_v3.py |  4 +++-
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/src/zarr/v3/group.py b/src/zarr/v3/group.py
index acd5ca0d62..4a84cbed80 100644
--- a/src/zarr/v3/group.py
+++ b/src/zarr/v3/group.py
@@ -4,7 +4,17 @@
 import asyncio
 import json
 import logging
-from typing import Any, Dict, Literal, Optional, Union, AsyncIterator, Iterator, List
+from typing import (
+    Any,
+    AsyncGenerator,
+    Dict,
+    Literal,
+    Optional,
+    Union,
+    AsyncIterator,
+    Iterator,
+    List,
+)
 from zarr.v3.abc.metadata import Metadata
 
 from zarr.v3.array import AsyncArray, Array
@@ -271,8 +281,29 @@ def __repr__(self):
     async def nchildren(self) -> int:
         raise NotImplementedError
 
-    async def children(self) -> AsyncIterator[AsyncArray, AsyncGroup]:
-        raise NotImplementedError
+    async def children(self) -> AsyncGenerator[AsyncArray, AsyncGroup]:
+        """
+        Returns an async iterator over the arrays and groups contained in this group.
+        """
+        if not self.store_path.store.supports_listing:
+            msg = (
+                f"The store associated with this group ({type(self.store_path.store)}) "
+                "does not support listing, "
+                "specifically the `list_dir` method. "
+                "This function requires a store that supports listing."
+            )
+
+            raise ValueError(msg)
+        subkeys = await self.store_path.store.list_dir(self.store_path.path)
+        # would be nice to make these special keys accessible programmatically,
+        # and scoped to specific zarr versions
+        subkeys_filtered = filter(lambda v: v not in ("zarr.json", ".zgroup", ".zattrs"), subkeys)
+        # might be smarter to wrap this in asyncio gather
+        for subkey in subkeys_filtered:
+            try:
+                yield await self.getitem(subkey)
+            except ValueError:
+                pass
 
     async def contains(self, child: str) -> bool:
         raise NotImplementedError
diff --git a/tests/test_group_v3.py b/tests/test_group_v3.py
index 1498d6779b..01859bb7ae 100644
--- a/tests/test_group_v3.py
+++ b/tests/test_group_v3.py
@@ -21,13 +21,15 @@ def test_group(store_path) -> None:
         runtime_configuration=RuntimeConfiguration(),
     )
     group = Group(agroup)
-
     assert agroup.metadata is group.metadata
 
     # create two groups
     foo = group.create_group("foo")
     bar = foo.create_group("bar", attributes={"baz": "qux"})
 
+    # check that bar is in the children of foo
+    assert foo.children == [bar]
+
     # create an array from the "bar" group
     data = np.arange(0, 4 * 4, dtype="uint16").reshape((4, 4))
     arr = bar.create_array(