add numcodecs.zarr3.to_zarr3 method

docs/release.rst

@@ -11,7 +11,6 @@ Release notes
     Unreleased
     ----------
 
-
 .. _unreleased:
 
 Unreleased
@@ -20,6 +19,9 @@ Unreleased
 Enhancements
 ~~~~~~~~~~~~
 
+* implement ``to_zarr3`` in ``numcodecs.zarr3`` to enable conversion of a codec to its zarr3-compatible equivalent.
+  By :user:`Hannes Spitz <brokkoli71>`
+
 Improvements
 ~~~~~~~~~~~~
 
@@ -63,7 +65,7 @@ Enhancements
 Removals
 ~~~~~~~~
 
-The following ``blosc`` funcitons are removed, with no replacement.
+The following ``blosc`` functions are removed, with no replacement.
 This is because they were not intended to be public API.
 
 - ``numcodecs.blosc.init``

numcodecs/tests/test_zarr3.py

@@ -4,6 +4,8 @@
 
 import numpy as np
 import pytest
+from zarr.abc.codec import ArrayArrayCodec, ArrayBytesCodec, BytesBytesCodec
+from zarr.core.array import CompressorsLike, FiltersLike, SerializerLike
 
 if TYPE_CHECKING:  # pragma: no cover
     import zarr
@@ -277,3 +279,65 @@
 def test_to_dict():
     codec = numcodecs.zarr3.LZ4(level=5)
     assert codec.to_dict() == {"name": "numcodecs.lz4", "configuration": {"level": 5}}
+
+
+@pytest.mark.parametrize(
+    ("codec_v2", "expected_v3_cls"),
+    [
+        (numcodecs.BZ2(), numcodecs.zarr3.BZ2),
+        (numcodecs.CRC32(), numcodecs.zarr3.CRC32),
+        (numcodecs.CRC32C(), numcodecs.zarr3.CRC32C),
+        (numcodecs.LZ4(), numcodecs.zarr3.LZ4),
+        (numcodecs.LZMA(), numcodecs.zarr3.LZMA),
+        (numcodecs.ZFPY(), numcodecs.zarr3.ZFPY),
+        (numcodecs.Adler32(), numcodecs.zarr3.Adler32),
+        (
+            numcodecs.AsType(encode_dtype=np.float64, decode_dtype=np.float32),
+            numcodecs.zarr3.AsType,
+        ),
+        (numcodecs.BitRound(keepbits=10), numcodecs.zarr3.BitRound),
+        (numcodecs.Blosc(), numcodecs.zarr3.Blosc),
+        (numcodecs.Delta(dtype=np.float64), numcodecs.zarr3.Delta),
+        (
+            numcodecs.FixedScaleOffset(offset=1000, scale=10, dtype='f8', astype='u1'),
+            numcodecs.zarr3.FixedScaleOffset,
+        ),
+        (numcodecs.Fletcher32(), numcodecs.zarr3.Fletcher32),
+        (numcodecs.GZip(), numcodecs.zarr3.GZip),
+        (numcodecs.JenkinsLookup3(), numcodecs.zarr3.JenkinsLookup3),
+        (numcodecs.PCodec(), numcodecs.zarr3.PCodec),
+        (numcodecs.PackBits(), numcodecs.zarr3.PackBits),
+        (numcodecs.Quantize(digits=1, dtype='f8'), numcodecs.zarr3.Quantize),
+        (numcodecs.Shuffle(), numcodecs.zarr3.Shuffle),
+        (numcodecs.Zlib(), numcodecs.zarr3.Zlib),
+        (numcodecs.Zstd(), numcodecs.zarr3.Zstd),
+    ],
+)
+def test_cast_numcodecs_to_v3(store: Store, codec_v2, expected_v3_cls) -> None:
+    result_v3 = numcodecs.zarr3.to_zarr3(codec_v2)
+
+    assert result_v3.__class__ == expected_v3_cls
+    assert result_v3.codec_config == codec_v2.get_config()
+
+    filters: FiltersLike = "auto"
+    serializer: SerializerLike = "auto"
+    compressors: CompressorsLike = "auto"
+    if isinstance(result_v3, ArrayArrayCodec):
+        filters = [result_v3]
+    elif isinstance(result_v3, ArrayBytesCodec):
+        serializer = result_v3
+    elif isinstance(result_v3, BytesBytesCodec):
+        compressors = [result_v3]
+    else:
+        raise TypeError(f"unsupported type: {result_v3.__class__}")
+
+    zarr.create_array(
+        store,
+        shape=(64,),
+        chunks=(64,),
+        dtype=np.bool,
+        fill_value=0,
+        filters=filters,
+        compressors=compressors,
+        serializer=serializer,
+    )

numcodecs/zarr3.py

@@ -399,3 +399,21 @@
     "Zlib",
     "Zstd",
 ]
+
+
+def to_zarr3(
+    codec: numcodecs.abc.Codec,
+) -> _NumcodecsBytesBytesCodec | _NumcodecsArrayBytesCodec | _NumcodecsArrayArrayCodec:
+    """Convert a numcodecs codec to its zarr3-compatible equivalent."""
+    codec_name = codec.__class__.__name__
+    zarr3_module = numcodecs.zarr3
+
+    if not hasattr(zarr3_module, codec_name):
+        raise ValueError(f"No Zarr3 wrapper found for codec: {codec_name}")
+
+    zarr3_codec_class = getattr(zarr3_module, codec_name)
+
+    config = codec.get_config()
+    config.pop("id", None)
+
+    return zarr3_codec_class(**config)