minimal Python error handling

Author: kylebarron

python/DEVELOP.md

@@ -1,6 +1,6 @@
 ```
 uv sync --no-install-package async-tiff
-uv run --no-project maturin develop
+uv run --no-project maturin develop --uv
 uv run --no-project mkdocs serve
-uv run --no-project pytest --verbose
+uv run --no-project pytest tests --verbose
 ```

python/pyproject.toml

@@ -32,13 +32,12 @@ dev-dependencies = [
     "mkdocstrings>=0.27.0",
     "numpy>=1",
     "obstore>=0.5.1",
-    "pip>=24.2",
     "pytest-asyncio>=0.26.0",
     "pytest>=8.3.3",
     "ruff>=0.8.4",
 ]
 
 [tool.pytest.ini_options]
 addopts = "--color=yes"
-asyncio_default_fixture_loop_scope="function"
+asyncio_default_fixture_loop_scope = "function"
 asyncio_mode = "auto"

python/src/error.rs

@@ -0,0 +1,43 @@
+use async_tiff::error::AsyncTiffError;
+use pyo3::create_exception;
+use pyo3::exceptions::PyFileNotFoundError;
+use pyo3::prelude::*;
+
+// Base exception
+// Note that this is named `BaseError` instead of `ObstoreError` to not leak the name "obstore" to
+// other Rust-Python libraries using pyo3-object_store.
+create_exception!(
+    async_tiff,
+    AsyncTiffException,
+    pyo3::exceptions::PyException,
+    "A general error from the underlying Rust async-tiff library."
+);
+
+#[allow(missing_docs)]
+pub enum PyAsyncTiffError {
+    AsyncTiffError(async_tiff::error::AsyncTiffError),
+}
+
+impl From<AsyncTiffError> for PyAsyncTiffError {
+    fn from(value: AsyncTiffError) -> Self {
+        Self::AsyncTiffError(value)
+    }
+}
+
+impl From<PyAsyncTiffError> for PyErr {
+    fn from(error: PyAsyncTiffError) -> Self {
+        match error {
+            PyAsyncTiffError::AsyncTiffError(err) => match err {
+                AsyncTiffError::ObjectStore(err) => match err {
+                    object_store::Error::NotFound { path: _, source: _ } => {
+                        PyFileNotFoundError::new_err(err.to_string())
+                    }
+                    _ => AsyncTiffException::new_err(err.to_string()),
+                },
+                _ => AsyncTiffException::new_err(err.to_string()),
+            },
+        }
+    }
+}
+
+pub type PyAsyncTiffResult<T> = std::result::Result<T, PyAsyncTiffError>;

python/src/lib.rs

@@ -2,6 +2,7 @@
 
 mod decoder;
 mod enums;
+mod error;
 mod geo;
 mod ifd;
 mod reader;

python/src/tiff.rs

@@ -9,6 +9,7 @@ use pyo3::prelude::*;
 use pyo3::types::PyType;
 use pyo3_async_runtimes::tokio::future_into_py;
 
+use crate::error::PyAsyncTiffResult;
 use crate::reader::StoreInput;
 use crate::tile::PyTile;
 use crate::PyImageFileDirectory;
@@ -19,6 +20,20 @@ pub(crate) struct PyTIFF {
     reader: Arc<dyn AsyncFileReader>,
 }
 
+async fn open(
+    reader: Arc<dyn AsyncFileReader>,
+    prefetch: u64,
+    multiplier: f64,
+) -> PyAsyncTiffResult<PyTIFF> {
+    let metadata_fetch = ReadaheadMetadataCache::new(reader.clone())
+        .with_initial_size(prefetch)
+        .with_multiplier(multiplier);
+    let mut metadata_reader = TiffMetadataReader::try_open(&metadata_fetch).await?;
+    let ifds = metadata_reader.read_all_ifds(&metadata_fetch).await?;
+    let tiff = TIFF::new(ifds);
+    Ok(PyTIFF { tiff, reader })
+}
+
 #[pymethods]
 impl PyTIFF {
     #[classmethod]
@@ -33,18 +48,11 @@ impl PyTIFF {
     ) -> PyResult<Bound<'py, PyAny>> {
         let reader = store.into_async_file_reader(path);
 
-        let cog_reader = future_into_py(py, async move {
-            let metadata_fetch = ReadaheadMetadataCache::new(reader.clone())
-                .with_initial_size(prefetch)
-                .with_multiplier(multiplier);
-            let mut metadata_reader = TiffMetadataReader::try_open(&metadata_fetch).await.unwrap();
-            let ifds = metadata_reader
-                .read_all_ifds(&metadata_fetch)
-                .await
-                .unwrap();
-            let tiff = TIFF::new(ifds);
-            Ok(PyTIFF { tiff, reader })
-        })?;
+        let cog_reader =
+            future_into_py(
+                py,
+                async move { Ok(open(reader, prefetch, multiplier).await?) },
+            )?;
         Ok(cog_reader)
     }