empty_like for object array raises warning

    import zarr
    z = zarr.empty(shape=(2,), dtype="array:u1")
    z[0] = [0, 1, 2]
    z[1] = [0, 0]
    print(z, z[:])
    y = zarr.empty_like(z) # Emits warning
    y[0] = [0, 1, 2]
    y[1] = [0, 0]
    print(y, y[:])

Gives:

<zarr.core.Array (2,) object> [array([0, 1, 2], dtype=uint8) array([0, 0], dtype=uint8)]
/home/jk/.local/lib/python3.5/site-packages/zarr/storage.py:372: FutureWarning: missing object_codec for object array; this will raise a ValueError in version 3.0
  'ValueError in version 3.0', FutureWarning)
<zarr.core.Array (2,) object> [array([0, 1, 2], dtype=uint8) array([0, 0], dtype=uint8)]

Problem description

It seems that empty_like is somehow not copying the codec? However, the array seems to behave perfectly well as a object array, so I’m not sure what’s happening.

Version and installation information

Please provide the following:

• Value of zarr.__version__: 2.2.0
• Value of numcodecs.__version__: 0.5.3
• Version of Python interpreter: 3.5.2
• Operating system (Linux/Windows/Mac): Linux
• How Zarr was installed (e.g., “using pip into virtual environment”, or “using conda”):pip

[hyanwong]

Yep thanks. Was ignoring it anyway 😃

[alimanfoo]

Thanks Jerome, this looks like just an API inconsistency, I didn’t properly consider the ..._like creation functions when writing the logic for how the object_codec keyword argument is handled. We should fix this so that no warning is emitted. For now you can ignore the warning, the array should be fine.