zarr.load deletes data

[alfieroddan]

Zarr version

3.0.7

Numcodecs version

0.16.0

Python Version

3.11.11

Operating System

MacOS

Installation

using pip into venv

Description

If I load a folder with zarr but there is no .zarray, it deletes my data! This is really not good and not obvious.

Is this intended or a bug?

I now know that the load function is not read only!

Instead use open_array with read only mode:

z = zarr.open_array(path, mode='r')

Steps to reproduce

(env) /Users/Documents/test_folder/video_2025-04-22_16-47-43-917 $ ls
zarr_folders rgb
(env) /Users/Documents/test_folder $ python 
Python 3.11.11 (main, Dec  3 2024, 17:20:40) [Clang 16.0.0 (clang-1600.0.26.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import zarr
>>> zarr.load("/Users/Documents/test_folder/video_2025-04-22_16-47-43-917")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/Documents/EnPlayback/env/lib/python3.11/site-packages/zarr/api/synchronous.py", line 151, in load
    return sync(
           ^^^^^
  File "/Users/Documents/EnPlayback/env/lib/python3.11/site-packages/zarr/core/sync.py", line 163, in sync
    raise return_result
  File "/Users/Documents/EnPlayback/env/lib/python3.11/site-packages/zarr/core/sync.py", line 119, in _runner
    return await coro
           ^^^^^^^^^^
  File "/Users/Documents/EnPlayback/env/lib/python3.11/site-packages/zarr/api/asynchronous.py", line 275, in load
    raise NotImplementedError("loading groups not yet supported")
NotImplementedError: loading groups not yet supported
(env) /Users/Documents/test_folder/video_2025-04-22_16-47-43-917 $ ls
zarr.json

Additional output

No response

[joshmoore]

can confirm

bar.py

# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "zarr",
# ]
# ///

import zarr
zarr.load("/tmp/bar")

setup and run

cd /tmp
mkdir bar
touch bar/IMPORTANT
uv run bar.py
Installed 5 packages in 10ms
Traceback (most recent call last):
  File "/private/tmp/bar.py", line 9, in <module>
    zarr.load("/tmp/bar")
    ~~~~~~~~~^^^^^^^^^^^^
  File "/Users/jamoore/.cache/uv/environments-v2/bar-1ba879a2e7d68a2e/lib/python3.13/site-packages/zarr/api/synchronous.py", line 151, in load
    return sync(
        async_api.load(store=store, zarr_version=zarr_version, zarr_format=zarr_format, path=path)
    )
  File "/Users/jamoore/.cache/uv/environments-v2/bar-1ba879a2e7d68a2e/lib/python3.13/site-packages/zarr/core/sync.py", line 163, in sync
    raise return_result
  File "/Users/jamoore/.cache/uv/environments-v2/bar-1ba879a2e7d68a2e/lib/python3.13/site-packages/zarr/core/sync.py", line 119, in _runner
    return await coro
           ^^^^^^^^^^
  File "/Users/jamoore/.cache/uv/environments-v2/bar-1ba879a2e7d68a2e/lib/python3.13/site-packages/zarr/api/asynchronous.py", line 275, in load
    raise NotImplementedError("loading groups not yet supported")
NotImplementedError: loading groups not yet supported

"IMPORTANT" is gone

$ find bar
bar
bar/zarr.json

Same results with:

# dependencies = [
#     "zarr @ git+https://github.com/zarr-developers/zarr-python.git#egg=zarr",
# ]

[d-v-b]

See a similar report in #2719

I think the acute fix is to ensure that load invokes open with mode=r

[FabricioArendTorres]

This seems like an absolutely major issue.

Is this only an issue for the LocalStore?

[d-v-b]

thanks for sorting this out @dstansby!

[dstansby]

Is this only an issue for the LocalStore?

I think (but haven't tested) that this issue affects all stores. We will try and get a release out with a fix later today, sorry for the pretty bad bug 😬