Use soft import strategy for optional dependencies see xarray/issues/…

…9554.

virtualizarr/readers/hdf/filters.py

@@ -1,24 +1,18 @@
 import dataclasses
-import warnings
 from typing import List, Tuple, TypedDict, Union
 
-import h5py  # type: ignore
 import numcodecs.registry as registry
 import numpy as np
 from numcodecs.abc import Codec
 from numcodecs.fixedscaleoffset import FixedScaleOffset
 from xarray.coding.variables import _choose_float_dtype
 
-try:
-    import hdf5plugin  # type: ignore
-except ModuleNotFoundError:
-    hdf5plugin = None  # type: ignore
-    warnings.warn("hdf5plugin is required for HDF reader")
+from virtualizarr.utils import soft_import
+
+h5py = soft_import("h5py", "For reading hdf files")
+hdf5plugin = soft_import("hdf5plugin", "For reading hdf files with filters")
+imagecodecs = soft_import("imagecodecs", "For reading hdf files with filters")
 
-try:
-    import imagecodecs  # noqa
-except ModuleNotFoundError:
-    warnings.warn("imagecodecs is required for HDF reader")
 
 _non_standard_filters = {
     "gzip": "zlib",

virtualizarr/readers/hdf/hdf.py

@@ -1,7 +1,6 @@
 import math
 from typing import Dict, Iterable, List, Mapping, Optional, Union
 
-import h5py  # type: ignore
 import numpy as np
 from xarray import Dataset, Index, Variable
 
@@ -13,9 +12,11 @@
 )
 from virtualizarr.readers.hdf.filters import cfcodec_from_dataset, codecs_from_dataset
 from virtualizarr.types import ChunkKey
-from virtualizarr.utils import _FsspecFSFromFilepath, check_for_collisions
+from virtualizarr.utils import _FsspecFSFromFilepath, check_for_collisions, soft_import
 from virtualizarr.zarr import ZArray
 
+h5py = soft_import("h5py", "For reading hdf files")
+
 
 class HDFVirtualBackend(VirtualBackend):
     @staticmethod

virtualizarr/utils.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import importlib
 import io
 from typing import TYPE_CHECKING, Iterable, Optional, Union
 
@@ -86,3 +87,16 @@ def check_for_collisions(
         raise ValueError(f"Cannot both load and drop variables {common}")
 
     return drop_variables, loadable_variables
+
+
+def soft_import(name: str, reason: str, strict: Optional[bool] = True):
+    try:
+        return importlib.import_module(name)
+    except (ImportError, ModuleNotFoundError):
+        if strict:
+            raise ImportError(
+                f"for {reason}, the {name} package is required. "
+                f"Please install it via pip or conda."
+            )
+        else:
+            return None