Refactor Windows DLL loading in Python packages

The existing space1d/space2d/space3d package initializers each
carried the same Windows DLL setup code before importing their
pybind extension. That logic only added the current package
directory plus entries already present on PATH via
os.add_dll_directory(). In practice this was fragile for wheel
installs because the extension import could still fail if
dependent DLLs were bundled in package-local locations that were
not already on PATH.

Centralize the DLL search setup in amrex._dll and call it from
each spaceNd package before importing amrex_*d_pybind. The new
helper prefers package-local locations first: the current
spaceNd directory, spaceNd/.libs, the parent amrex package
directory, and amrex/.libs. It then falls back to PATH for
source and developer installs.

Keep the os.add_dll_directory() handles alive for the lifetime
of the process and deduplicate discovered paths. This keeps the
Windows import workaround in one place and makes it compatible
with vendored wheel layouts as well as traditional shared-
library installs.

Author: ax3l

src/amrex/_dll.py

@@ -0,0 +1,63 @@
+# -*- coding: utf-8 -*-
+
+import os
+from pathlib import Path
+
+_DLL_DIRECTORY_HANDLES = {}
+
+
+def _iter_windows_dll_directories(package_file):
+    package_dir = Path(package_file).resolve().parent
+    package_root = package_dir.parent
+    seen = set()
+
+    candidates = (
+        package_dir,
+        package_dir / ".libs",
+        package_root,
+        package_root / ".libs",
+    )
+
+    for candidate in candidates:
+        if candidate.is_dir():
+            candidate_str = str(candidate)
+            if candidate_str not in seen:
+                seen.add(candidate_str)
+                yield candidate_str
+
+    for entry in os.environ.get("PATH", "").split(os.pathsep):
+        if not entry:
+            continue
+
+        path = Path(os.path.expandvars(os.path.expanduser(entry)))
+        try:
+            resolved = path.resolve()
+        except OSError:
+            continue
+
+        if not resolved.exists():
+            continue
+
+        resolved_str = str(resolved)
+        if resolved_str not in seen:
+            seen.add(resolved_str)
+            yield resolved_str
+
+
+def add_windows_dll_directories(package_file):
+    """Keep DLL directories registered for the lifetime of the process."""
+    if os.name != "nt" or not hasattr(os, "add_dll_directory"):
+        return
+
+    package_dir = str(Path(package_file).resolve().parent)
+    if package_dir in _DLL_DIRECTORY_HANDLES:
+        return
+
+    handles = []
+    for dll_dir in _iter_windows_dll_directories(package_file):
+        try:
+            handles.append(os.add_dll_directory(dll_dir))
+        except OSError:
+            continue
+
+    _DLL_DIRECTORY_HANDLES[package_dir] = handles

src/amrex/space1d/__init__.py

@@ -1,22 +1,8 @@
 # -*- coding: utf-8 -*-
 
-import os
-
-# Python 3.8+ on Windows: DLL search paths for dependent
-# shared libraries
-# Refs.:
-# - https://github.com/python/cpython/issues/80266
-# - https://docs.python.org/3.8/library/os.html#os.add_dll_directory
-if os.name == "nt":
-    # add anything in the current directory
-    pwd = __file__.rsplit(os.sep, 1)[0] + os.sep
-    os.add_dll_directory(pwd)
-    # add anything in PATH
-    paths = os.environ.get("PATH", "")
-    for p in paths.split(";"):
-        p_abs = os.path.abspath(os.path.expanduser(os.path.expandvars(p)))
-        if os.path.exists(p_abs):
-            os.add_dll_directory(p_abs)
+from .._dll import add_windows_dll_directories
+
+add_windows_dll_directories(__file__)
 
 # import core bindings to C++
 from . import amrex_1d_pybind

src/amrex/space2d/__init__.py

@@ -1,22 +1,8 @@
 # -*- coding: utf-8 -*-
 
-import os
-
-# Python 3.8+ on Windows: DLL search paths for dependent
-# shared libraries
-# Refs.:
-# - https://github.com/python/cpython/issues/80266
-# - https://docs.python.org/3.8/library/os.html#os.add_dll_directory
-if os.name == "nt":
-    # add anything in the current directory
-    pwd = __file__.rsplit(os.sep, 1)[0] + os.sep
-    os.add_dll_directory(pwd)
-    # add anything in PATH
-    paths = os.environ.get("PATH", "")
-    for p in paths.split(";"):
-        p_abs = os.path.abspath(os.path.expanduser(os.path.expandvars(p)))
-        if os.path.exists(p_abs):
-            os.add_dll_directory(p_abs)
+from .._dll import add_windows_dll_directories
+
+add_windows_dll_directories(__file__)
 
 # import core bindings to C++
 from . import amrex_2d_pybind

src/amrex/space3d/__init__.py

@@ -1,22 +1,8 @@
 # -*- coding: utf-8 -*-
 
-import os
-
-# Python 3.8+ on Windows: DLL search paths for dependent
-# shared libraries
-# Refs.:
-# - https://github.com/python/cpython/issues/80266
-# - https://docs.python.org/3.8/library/os.html#os.add_dll_directory
-if os.name == "nt":
-    # add anything in the current directory
-    pwd = __file__.rsplit(os.sep, 1)[0] + os.sep
-    os.add_dll_directory(pwd)
-    # add anything in PATH
-    paths = os.environ.get("PATH", "")
-    for p in paths.split(";"):
-        p_abs = os.path.abspath(os.path.expanduser(os.path.expandvars(p)))
-        if os.path.exists(p_abs):
-            os.add_dll_directory(p_abs)
+from .._dll import add_windows_dll_directories
+
+add_windows_dll_directories(__file__)
 
 # import core bindings to C++
 from . import amrex_3d_pybind