zarr.group raises FileNotFoundError

[K-Meech]

Zarr version

latest main

Numcodecs version

v0.16.1

Python Version

3.13

Operating System

Windows

Installation

pip install into a virtual environment

Description

On the latest main branch, zarr.group raises a FileNotFoundError when creating a new group - see example code below.

Error:

File "C:\Users\kimme\Documents\Repos\forked\zarr-python\src\zarr\storage\_common.py", line 361, in make_store_path
    store = await LocalStore.open(root=store_like, mode=mode)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\kimme\Documents\Repos\forked\zarr-python\src\zarr\storage\_local.py", line 142, in open
    await store._open()
  File "C:\Users\kimme\Documents\Repos\forked\zarr-python\src\zarr\storage\_local.py", line 154, in _open
    raise FileNotFoundError(f"{self.root} does not exist")
FileNotFoundError: data\example.zarr does not exist

Steps to reproduce

# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "zarr@git+https://github.com/zarr-developers/zarr-python.git@main",
# ]
# ///
#
# This script automatically imports the development branch of zarr to check for issues

import zarr
root = zarr.group('data/example.zarr')

Additional output

No response

[d-v-b]

can you test this with 3.1.1? I wonder if somehow this slipped in via #3307

[K-Meech]

I tried with 3.1.1 and there is no error raised there.

[dstansby]

😬 thanks for uncovering this, and it's not great that we don't test for it!

My PR seems to have uncovered an issue in how groups are created; I believe this is the fix, but I don't have time to write a test that fails before the change at the moment, so others please feel free to open a PR with the fix and a test!

diff --git a/src/zarr/api/asynchronous.py b/src/zarr/api/asynchronous.py
index fdbd3b34..55249236 100644
--- a/src/zarr/api/asynchronous.py
+++ b/src/zarr/api/asynchronous.py
@@ -677,7 +677,7 @@ async def group(
     if overwrite:
         mode = "w"
     else:
-        mode = "r+"
+        mode = "w-"
     store_path = await make_store_path(store, path=path, mode=mode, storage_options=storage_options)
 
     if chunk_store is not None:

[d-v-b]

@dstansby I posted a PR with your proposed change, and some tests, here: #3426. Unfortunately, fixing this particular bug triggers test failures elsewhere in the codebase. Store permissions really is the gift that keeps on giving.