Add nodata attribute to Raster

src/snaphu/io/_raster.py

@@ -97,6 +97,7 @@ def create(
         driver: str | None = None,
         crs: str | Mapping[str, str] | rasterio.crs.CRS | None = None,
         transform: rasterio.transform.Affine | None = None,
+        nodata: float | None = None,
         *,
         like: Raster | None = None,
         **kwargs: Any,
@@ -135,6 +136,11 @@ def create(
             Affine transformation mapping the pixel space to geographic space. If None,
             the geotransform of `like` will be used, if available, otherwise the default
             transform will be used. Defaults to None.
+        nodata : float or None, optional
+            Defines the pixel value to be interpreted as not valid data. If None, the
+            nodata value of `like` will be used, if available, otherwise no nodata value
+            will be populated. Only real-valued nodata values are supported, even if the
+            raster data is complex-valued. Defaults to None.
         like : Raster or None, optional
             An optional reference raster. If not None, the new raster will be created
             with the same metadata (shape, data-type, driver, CRS/geotransform, etc) as
@@ -158,6 +164,8 @@ def create(
             kwargs["crs"] = crs
         if transform is not None:
             kwargs["transform"] = transform
+        if nodata is not None:
+            kwargs["nodata"] = nodata
 
         # Always create a single-band dataset, even if `like` was part of a multi-band
         # dataset.
@@ -233,6 +241,15 @@ def transform(self) -> rasterio.transform.Affine:
         """
         return self.dataset.transform
 
+    @property
+    def nodata(self) -> float | None:
+        """
+        float or None : The raster's nodata value (may be unset).
+
+        The raster's nodata value, or None if no nodata value was set.
+        """
+        return self.dataset.nodatavals[self.band - 1]  # type: ignore[no-any-return]
+
     @property
     def closed(self) -> bool:
         """bool : True if the dataset is closed."""  # noqa: D403

test/io/test_raster.py

@@ -14,6 +14,9 @@
 
 import snaphu
 
+# Maximum value representable by 32-bit unsigned integer type.
+UINT32_MAX = np.iinfo(np.uint32).max
+
 
 def has_rasterio() -> bool:
     """Check if `rasterio` can be imported."""
@@ -27,6 +30,7 @@ def make_geotiff_raster(
     dtype: DTypeLike = np.int32,
     epsg: int = 4326,
     extents: tuple[float, float, float, float] = (0.0, 0.0, 1.0, 1.0),
+    nodata: float | None = None,
 ) -> Generator[snaphu.io.Raster, None, None]:
     """
     Make a dummy GeoTiff raster for testing.
@@ -47,6 +51,8 @@ def make_geotiff_raster(
         The geospatial extents of the raster image, in coordinates defined by the CRS
         represented by the `epsg` code, in the following order: West, South, East,
         North.
+    nodata : float or None, optional
+        Defines the pixel value to be interpreted as not valid data.
 
     Yields
     ------
@@ -65,6 +71,7 @@ def make_geotiff_raster(
         dtype=dtype,
         crs=crs,
         transform=transform,
+        nodata=nodata,
         driver="GTiff",
     ) as raster:
         yield raster
@@ -179,6 +186,23 @@ def test_transform(self, geotiff_raster: snaphu.io.Raster):
         transform = rasterio.transform.from_bounds(0.0, 0.0, 1.0, 1.0, width, height)
         assert geotiff_raster.transform == transform
 
+    @pytest.mark.parametrize(
+        ("dtype", "nodata"),
+        [
+            (np.int32, -999.0),
+            (np.uint32, UINT32_MAX),
+            (np.float64, 123.456),
+            (np.complex64, 0.0),
+            (np.float32, None),
+        ],
+    )
+    def test_nodata(self, dtype: DTypeLike, nodata: float | None):
+        with (
+            tempfile.NamedTemporaryFile(suffix=".tif") as file_,
+            make_geotiff_raster(file_.name, dtype=dtype, nodata=nodata) as raster,
+        ):
+            assert raster.nodata == nodata
+
     def test_open_closed(self):
         with make_temp_geotiff_raster() as raster:
             assert not raster.closed