allow int-like floats for int dtype fill values

changes/3448.bugfix.rst

@@ -0,0 +1,3 @@
+Setting ``fill_value`` to a float like ``0.0`` when the data type of the array is an integer is a common
+mistake. This change lets Zarr Python read arrays with this erroneous metadata, although Zarr Python
+will not create such arrays.

src/zarr/core/dtype/npy/common.py

@@ -9,6 +9,7 @@
     Any,
     Final,
     Literal,
+    NewType,
     SupportsComplex,
     SupportsFloat,
     SupportsIndex,
@@ -54,6 +55,9 @@
     "generic",
 )
 
+IntishFloat = NewType("IntishFloat", float)
+"""A type for floats that represent integers, like 1.0 (but not 1.1)."""
+
 NumpyEndiannessStr = Literal[">", "<", "="]
 NUMPY_ENDIANNESS_STR: Final = ">", "<", "="
 
@@ -467,6 +471,23 @@ def check_json_int(data: JSON) -> TypeGuard[int]:
     return bool(isinstance(data, int))
 
 
+def check_json_intish_float(data: JSON) -> TypeGuard[IntishFloat]:
+    """
+    Check if a JSON value is an "intish float", i.e. a float that represents an integer, like 0.0.
+
+    Parameters
+    ----------
+    data : JSON
+        The JSON value to check.
+
+    Returns
+    -------
+    Bool
+        True if the data is an intish float, False otherwise.
+    """
+    return isinstance(data, float) and data.is_integer()
+
+
 def check_json_str(data: JSON) -> TypeGuard[str]:
     """
     Check if a JSON value is a string.

src/zarr/core/dtype/npy/int.py

@@ -25,6 +25,7 @@
 )
 from zarr.core.dtype.npy.common import (
     check_json_int,
+    check_json_intish_float,
     endianness_to_numpy_str,
     get_endianness_from_numpy_dtype,
 )
@@ -206,6 +207,8 @@ def from_json_scalar(self, data: JSON, *, zarr_format: ZarrFormat) -> TIntScalar
         """
         if check_json_int(data):
             return self._cast_scalar_unchecked(data)
+        if check_json_intish_float(data):
+            return self._cast_scalar_unchecked(int(data))
         raise TypeError(f"Invalid type: {data}. Expected an integer.")
 
     def to_json_scalar(self, data: object, *, zarr_format: ZarrFormat) -> int:

tests/test_dtype/test_npy/test_common.py

@@ -20,6 +20,7 @@
     check_json_float_v2,
     check_json_float_v3,
     check_json_int,
+    check_json_intish_float,
     check_json_str,
     complex_float_to_json_v2,
     complex_float_to_json_v3,
@@ -320,6 +321,12 @@ def test_check_json_int() -> None:
     assert not check_json_int(1.0)
 
 
+def test_check_json_intish_float() -> None:
+    assert check_json_intish_float(0.0)
+    assert check_json_intish_float(1.0)
+    assert not check_json_intish_float("0")
+
+
 def test_check_json_str() -> None:
     assert check_json_str("0")
     assert not check_json_str(1.0)

tests/test_dtype/test_npy/test_int.py

@@ -28,7 +28,7 @@ class TestInt8(BaseTestZDType):
         {"name": "int8", "configuration": {"endianness": "little"}},
     )
 
-    scalar_v2_params = ((Int8(), 1), (Int8(), -1))
+    scalar_v2_params = ((Int8(), 1), (Int8(), -1), (Int8(), 1.0))
     scalar_v3_params = ((Int8(), 1), (Int8(), -1))
     cast_value_params = (
         (Int8(), 1, np.int8(1)),
@@ -63,7 +63,7 @@ class TestInt16(BaseTestZDType):
         {"name": "int16", "configuration": {"endianness": "little"}},
     )
 
-    scalar_v2_params = ((Int16(), 1), (Int16(), -1))
+    scalar_v2_params = ((Int16(), 1), (Int16(), -1), (Int16(), 1.0))
     scalar_v3_params = ((Int16(), 1), (Int16(), -1))
     cast_value_params = (
         (Int16(), 1, np.int16(1)),
@@ -101,7 +101,7 @@ class TestInt32(BaseTestZDType):
         {"name": "int32", "configuration": {"endianness": "little"}},
     )
 
-    scalar_v2_params = ((Int32(), 1), (Int32(), -1))
+    scalar_v2_params = ((Int32(), 1), (Int32(), -1), (Int32(), 1.0))
     scalar_v3_params = ((Int32(), 1), (Int32(), -1))
     cast_value_params = (
         (Int32(), 1, np.int32(1)),
@@ -136,7 +136,7 @@ class TestInt64(BaseTestZDType):
         {"name": "int64", "configuration": {"endianness": "little"}},
     )
 
-    scalar_v2_params = ((Int64(), 1), (Int64(), -1))
+    scalar_v2_params = ((Int64(), 1), (Int64(), -1), (Int64(), 1.0))
     scalar_v3_params = ((Int64(), 1), (Int64(), -1))
     cast_value_params = (
         (Int64(), 1, np.int64(1)),
@@ -168,7 +168,7 @@ class TestUInt8(BaseTestZDType):
         {"name": "uint8", "configuration": {"endianness": "little"}},
     )
 
-    scalar_v2_params = ((UInt8(), 1), (UInt8(), 0))
+    scalar_v2_params = ((UInt8(), 1), (UInt8(), 0), (UInt8(), 1.0))
     scalar_v3_params = ((UInt8(), 1), (UInt8(), 0))
     cast_value_params = (
         (UInt8(), 1, np.uint8(1)),
@@ -203,7 +203,7 @@ class TestUInt16(BaseTestZDType):
         {"name": "uint16", "configuration": {"endianness": "little"}},
     )
 
-    scalar_v2_params = ((UInt16(), 1), (UInt16(), 0))
+    scalar_v2_params = ((UInt16(), 1), (UInt16(), 0), (UInt16(), 1.0))
     scalar_v3_params = ((UInt16(), 1), (UInt16(), 0))
     cast_value_params = (
         (UInt16(), 1, np.uint16(1)),
@@ -238,7 +238,7 @@ class TestUInt32(BaseTestZDType):
         {"name": "uint32", "configuration": {"endianness": "little"}},
     )
 
-    scalar_v2_params = ((UInt32(), 1), (UInt32(), 0))
+    scalar_v2_params = ((UInt32(), 1), (UInt32(), 0), (UInt32(), 1.0))
     scalar_v3_params = ((UInt32(), 1), (UInt32(), 0))
     cast_value_params = (
         (UInt32(), 1, np.uint32(1)),
@@ -273,7 +273,7 @@ class TestUInt64(BaseTestZDType):
         {"name": "uint64", "configuration": {"endianness": "little"}},
     )
 
-    scalar_v2_params = ((UInt64(), 1), (UInt64(), 0))
+    scalar_v2_params = ((UInt64(), 1), (UInt64(), 0), (UInt64(), 1.0))
     scalar_v3_params = ((UInt64(), 1), (UInt64(), 0))
     cast_value_params = (
         (UInt64(), 1, np.uint64(1)),