(fix): add check for typesize<1

Author: ilan-gold

numcodecs/blosc.pyx

@@ -279,7 +279,9 @@ def compress(source, char* cname, int clevel, int shuffle=SHUFFLE,
     source_buffer = Buffer(source, PyBUF_ANY_CONTIGUOUS)
     source_ptr = source_buffer.ptr
     nbytes = source_buffer.nbytes
-    if typesize is not None:
+    if isinstance(typesize, int):
+        if typesize < 1:
+            raise ValueError(f"Cannot use typesize {typesize} less than 1.")
         itemsize = typesize
     else:
         itemsize = source_buffer.itemsize
@@ -572,6 +574,8 @@ class Blosc(Codec):
     max_buffer_size = 2**31 - 1
 
     def __init__(self, cname='lz4', clevel=5, shuffle=SHUFFLE, blocksize=AUTOBLOCKS, typesize=None):
+        if isinstance(typesize, int) and typesize < 1:
+            raise ValueError(f"Cannot use typesize {typesize} less than 1.")
         self.cname = cname
         if isinstance(cname, str):
             self._cname_bytes = cname.encode('ascii')

numcodecs/tests/test_blosc.py

@@ -285,3 +285,8 @@ def test_typesize_explicit():
     # third byte encodes the `typesize`
     assert encoded_without_itemsize[3] == 1  # inferred from bytes i.e., 1
     assert encoded_with_itemsize[3] == itemsize  # given as a constructor argument
+
+
+def test_typesize_less_than_1():
+    with pytest.raises(ValueError, match=r"Cannot use typesize"):
+        Blosc(shuffle=Blosc.SHUFFLE, typesize=0)