TypeError: Expected a BytesBytesCodec. Got <class 'numcodecs.blosc.Blosc'> instead.

[leoniewgnr]

This code runs without any problems with zarr2, but give the following error when running with zarr3:

import pandas as pd
import numpy as np
import xarray as xr
from numcodecs.blosc import Blosc

ds = xr.Dataset(
    {"foo": (("x", "y"), np.random.rand(4, 5))},
    coords={
        "x": [10, 20, 30, 40],
        "y": pd.date_range("2000-01-01", periods=5),
        "z": ("x", list("abcd")),
    },
)

tmp_path = 'tmp.zarr'

# this works
ds.to_zarr(tmp_path, mode="w")
print('Saved to tmp.zarr')

# this does not work 
compressor = Blosc(cname="zstd", clevel=3, shuffle=2)
ds.to_zarr(tmp_path, encoding={"foo": {"compressor": compressor}}, mode="w")
print('Saved to tmp.zarr')

The error message is: TypeError: Expected a BytesBytesCodec. Got <class 'numcodecs.blosc.Blosc'> instead.
The same error occurs in the documentation: https://docs.xarray.dev/en/stable/user-guide/io.html#zarr-compressors-and-filters

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[TomNicholas]

Thanks for raising this @leoniewgnr ! We're still hunting down all the bugs that the move to zarr 3 created.

The same error occurs in the documentation:

That's particularly weird - errors in the documentation examples are supposed to lead to errors in the CI...

[keewis]

See also #9987

[FedeMPouzols]

I think this example needs to be updated for zarr-python 3. Something like this works for me:

diff --git a/doc/user-guide/io.rst b/doc/user-guide/io.rst
index 986d43ce..7f5d6e2b 100644
--- a/doc/user-guide/io.rst
+++ b/doc/user-guide/io.rst
@@ -829,10 +829,10 @@ For example:
     :okwarning:
 
     import zarr
-    from numcodecs.blosc import Blosc
+    from zarr.codecs import BloscCodec
 
-    compressor = Blosc(cname="zstd", clevel=3, shuffle=2)
-    ds.to_zarr("foo.zarr", encoding={"foo": {"compressor": compressor}})
+    compressor = BloscCodec(cname="zstd", clevel=3, shuffle="shuffle")
+    ds.to_zarr("foo.zarr", encoding={"foo": {"compressors": (compressor,)}})
 
 .. note::

(this is my best guess based on what I see in the backend tests some Zarr v3 related PRs. In this particular case, {"compressor": compressor} (without tuple) seems to also work.).

Perhaps @d-v-b can confirm this is now the proper way to specify encoders/help with this?

[d-v-b]

that looks right, although I'm not too familiar with what ds.to_zarr is doing under the hood. The basic idea in zarr v3 is that there can be multiple codecs that transform an array after it has been flattened to a byte stream (alternately called "compressors" or "BytesBytesCodec"), hence the tuple. but we also accept a single codec, which we will wrap in a tuple.

[fowlerovski]

My situation with numcodecs 0.15.1 and Zarr 3.0.3 mirrors this: BytesBytesCodec is unavailable in numcodecs.abc, and even numcodecs.Blosc is rejected with TypeError: Expected a BytesBytesCodec.

[roansong]

I'm running into this as well, even when using numcodecs.zarr3.Blosc or zarr.codecs.BloscCodec.