Cleanup crc32c soft dependency

Author: jakirkham

numcodecs/__init__.py

@@ -117,13 +117,17 @@
 
     register_codec(MsgPack)
 
-from numcodecs.checksum32 import CRC32, CRC32C, Adler32, JenkinsLookup3
+from numcodecs.checksum32 import CRC32, Adler32, JenkinsLookup3
 
 register_codec(CRC32)
-register_codec(CRC32C)
 register_codec(Adler32)
 register_codec(JenkinsLookup3)
 
+with suppress(ImportError):
+    from numcodecs.checksum32 import CRC32C
+
+    register_codec(CRC32C)
+
 from numcodecs.json import JSON
 
 register_codec(JSON)

numcodecs/checksum32.py

@@ -1,14 +1,20 @@
 import struct
 import zlib
 from collections.abc import Callable
-from typing import TYPE_CHECKING, Literal
+from contextlib import suppress
+from types import ModuleType
+from typing import TYPE_CHECKING, Literal, Optional
 
 import numpy as np
 
 from .abc import Codec
 from .compat import ensure_contiguous_ndarray, ndarray_copy
 from .jenkins import jenkins_lookup3
 
+_crc32c: Optional[ModuleType] = None
+with suppress(ImportError):
+    import crc32c as _crc32c
+
 if TYPE_CHECKING:
     from typing_extensions import Buffer
 
@@ -76,28 +82,6 @@ class CRC32(Checksum32):
     location = 'start'
 
 
-class CRC32C(Checksum32):
-    """Codec add a crc32c checksum to the buffer.
-
-    Parameters
-    ----------
-    location : 'start' or 'end'
-        Where to place the checksum in the buffer.
-    """
-
-    codec_id = 'crc32c'
-
-    def checksum(self, buf):
-        try:
-            from crc32c import crc32c as crc32c_
-
-            return crc32c_(buf)
-        except ImportError:  # pragma: no cover
-            raise ImportError("crc32c must be installed to use the CRC32C checksum codec.")
-
-    location = 'end'
-
-
 class Adler32(Checksum32):
     """Codec add a adler32 checksum to the buffer.
 
@@ -168,3 +152,20 @@ def decode(self, buf, out=None):
             out.view("uint8")[:] = b[:-4]
             return out
         return memoryview(b[:-4])
+
+
+if _crc32c:
+
+    class CRC32C(Checksum32):
+        """Codec add a crc32c checksum to the buffer.
+
+        Parameters
+        ----------
+        location : 'start' or 'end'
+            Where to place the checksum in the buffer.
+        """
+
+        codec_id = 'crc32c'
+
+        checksum = _crc32c.crc32c
+        location = 'end'

numcodecs/tests/test_checksum32.py

@@ -1,13 +1,10 @@
 import itertools
+from contextlib import suppress
 
 import numpy as np
 import pytest
 
-try:
-    from numcodecs.checksum32 import CRC32, CRC32C, Adler32
-except ImportError:  # pragma: no cover
-    pytest.skip("numcodecs.checksum32 not available", allow_module_level=True)
-
+from numcodecs.checksum32 import CRC32, Adler32
 from numcodecs.tests.common import (
     check_backwards_compatibility,
     check_config,
@@ -17,6 +14,12 @@
     check_repr,
 )
 
+has_crc32c = False
+with suppress(ImportError):
+    from numcodecs.checksum32 import CRC32C
+
+    has_crc32c = True
+
 # mix of dtypes: integer, float, bool, string
 # mix of shapes: 1D, 2D, 3D
 # mix of orders: C, F
@@ -39,11 +42,16 @@
 codecs = [
     CRC32(),
     CRC32(location="end"),
-    CRC32C(location="start"),
-    CRC32C(),
     Adler32(),
     Adler32(location="end"),
 ]
+if has_crc32c:
+    codecs.extend(
+        [
+            CRC32C(location="start"),
+            CRC32C(),
+        ]
+    )
 
 
 @pytest.mark.parametrize(("codec", "arr"), itertools.product(codecs, arrays))
@@ -88,25 +96,28 @@ def test_err_encode_list(codec):
 def test_err_location():
     with pytest.raises(ValueError):
         CRC32(location="foo")
-    with pytest.raises(ValueError):
-        CRC32C(location="foo")
     with pytest.raises(ValueError):
         Adler32(location="foo")
+    if has_crc32c:
+        with pytest.raises(ValueError):
+            CRC32C(location="foo")
 
 
 def test_repr():
     check_repr("CRC32(location='start')")
-    check_repr("CRC32C(location='start')")
-    check_repr("Adler32(location='start')")
     check_repr("CRC32(location='end')")
-    check_repr("CRC32C(location='end')")
+    check_repr("Adler32(location='start')")
     check_repr("Adler32(location='end')")
+    if has_crc32c:
+        check_repr("CRC32C(location='start')")
+        check_repr("CRC32C(location='end')")
 
 
 def test_backwards_compatibility():
     check_backwards_compatibility(CRC32.codec_id, arrays, [CRC32()])
     check_backwards_compatibility(Adler32.codec_id, arrays, [Adler32()])
-    check_backwards_compatibility(CRC32C.codec_id, arrays, [CRC32C()])
+    if has_crc32c:
+        check_backwards_compatibility(CRC32C.codec_id, arrays, [CRC32C()])
 
 
 @pytest.mark.parametrize("codec", codecs)
@@ -127,6 +138,7 @@ def test_err_out_too_small(codec):
         codec.decode(codec.encode(arr), out)
 
 
+@pytest.mark.skipif(not has_crc32c, reason="Needs `crc32c` installed")
 def test_crc32c_checksum():
     arr = np.arange(0, 64, dtype="uint8")
     buf = CRC32C(location="end").encode(arr)