python: Fix Windows pyd directory and manage new python 3.8 rule to import a library on Windows

Author: jorisv

python/CMakeLists.txt

@@ -36,6 +36,8 @@ SET_TARGET_PROPERTIES(${PYWRAP}
   SUFFIX ${PYTHON_EXT_SUFFIX}
   OUTPUT_NAME "${PYWRAP}"
   LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/python/${PROJECT_NAME}"
+  # On Windows, shared library are treated as binary
+  RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/python/${PROJECT_NAME}"
   )
 
 IF(UNIX AND NOT APPLE)
@@ -47,6 +49,7 @@ INSTALL(TARGETS ${PYWRAP} DESTINATION ${${PYWRAP}_INSTALL_DIR})
 # --- INSTALL SCRIPTS
 SET(PYTHON_FILES
   __init__.py
+  windows_dll_manager.py
   )
 
 FOREACH(python ${PYTHON_FILES})

python/pycppad/__init__.py

@@ -4,3 +4,30 @@
 
 from .pycppad_pywrap import *
 from .pycppad_pywrap import __version__, __raw_version__
+
+# On Windows, if pycppad.dll is not in the same directory than
+# the .pyd, it will not be loaded.
+# We first try to load pycppad, then, if it fail and we are on Windows:
+#  1. We add all paths inside PYCPPAD_WINDOWS_DLL_PATH to DllDirectory
+#  2. If PYCPPAD_WINDOWS_DLL_PATH we add the relative path from the
+#     package directory to the bin directory to DllDirectory
+# This solution is inspired from:
+#  - https://github.com/PixarAnimationStudios/OpenUSD/pull/1511/files
+#  - https://stackoverflow.com/questions/65334494/python-c-extension-packaging-dll-along-with-pyd
+# More resources on https://github.com/diffpy/pyobjcryst/issues/33
+try:
+    from .pycppad_pywrap import *
+    from .pycppad_pywrap import __version__, __raw_version__
+except ImportError:
+    import platform
+
+    if platform.system() == "Windows":
+        from .windows_dll_manager import get_dll_paths, build_directory_manager
+
+        with build_directory_manager() as dll_dir_manager:
+            for p in get_dll_paths():
+                dll_dir_manager.add_dll_directory(p)
+            from .pycppad_pywrap import *
+            from .pycppad_pywrap import __version__, __raw_version__
+    else:
+        raise

python/pycppad/windows_dll_manager.py

@@ -0,0 +1,65 @@
+import os
+import sys
+import contextlib
+
+
+def get_dll_paths():
+    pycppad_paths = os.getenv("PYCPPAD_WINDOWS_DLL_PATH")
+    if pycppad_paths is None:
+        # From https://peps.python.org/pep-0250/#implementation
+        # lib/python-version/site-packages/package
+        RELATIVE_DLL_PATH1 = "..\\..\\..\\..\\bin"
+        # lib/site-packages/package
+        RELATIVE_DLL_PATH2 = "..\\..\\..\\bin"
+        # For unit test
+        RELATIVE_DLL_PATH3 = "..\\..\\bin"
+        return [
+            os.path.join(os.path.dirname(__file__), RELATIVE_DLL_PATH1),
+            os.path.join(os.path.dirname(__file__), RELATIVE_DLL_PATH2),
+            os.path.join(os.path.dirname(__file__), RELATIVE_DLL_PATH3),
+        ]
+    else:
+        return pycppad_paths.split(os.pathsep)
+
+
+class PathManager(contextlib.AbstractContextManager):
+    """Restore PATH state after importing Python module"""
+
+    def add_dll_directory(self, dll_dir: str):
+        os.environ["PATH"] += os.pathsep + dll_dir
+
+    def __enter__(self):
+        self.old_path = os.environ["PATH"]
+        return self
+
+    def __exit__(self, *exc_details):
+        os.environ["PATH"] = self.old_path
+
+
+class DllDirectoryManager(contextlib.AbstractContextManager):
+    """Restore DllDirectory state after importing Python module"""
+
+    def add_dll_directory(self, dll_dir: str):
+        # add_dll_directory can fail on relative path and non
+        # existing path.
+        # Since we don't know all the fail criterion we just ignore
+        # thrown exception
+        try:
+            self.dll_dirs.append(os.add_dll_directory(dll_dir))
+        except OSError:
+            pass
+
+    def __enter__(self):
+        self.dll_dirs = []
+        return self
+
+    def __exit__(self, *exc_details):
+        for d in self.dll_dirs:
+            d.close()
+
+
+def build_directory_manager():
+    if sys.version_info >= (3, 8):
+        return DllDirectoryManager()
+    else:
+        return PathManager()