Importing python bindings works when using conda in windows thanks to…

… Joris Vaillant !

modules/python/bindings/visp/__init__.py

@@ -40,15 +40,21 @@
 # print(sys.path)
 
 
-# On windows, we need to explicitely add paths where Python should look for DLLs (This starts with Python >= 3.8)
-LOADER_DIR = os.path.dirname(os.path.abspath(os.path.realpath(__file__)))
-
-
-
-
-
-import _visp
-from _visp import *
+try:
+  import _visp
+  from _visp import *
+except ImportError:
+  import platform
+  if platform.system() == "Windows": # On windows import can fail because DLLs are not found in the default search paths
+    from .windows_dll_manager import get_dll_paths, build_directory_manager
+    # Use the context to clean up the PATH/dll directories after the import (no namespace pollution)
+    with build_directory_manager() as dll_dir_manager:
+      for p in get_dll_paths():
+        dll_dir_manager.add_dll_directory(p)
+      import _visp
+      from _visp import *
+  else:
+    raise
 
 # Fake module names
 for k in _visp.__dict__:

modules/python/bindings/visp/windows-dll-manager.py

@@ -0,0 +1,75 @@
+'''
+This code is directly adapted from proxsuite_nlp, see:
+
+- https://github.com/Simple-Robotics/proxsuite-nlp/blob/main/bindings/python/proxsuite_nlp/windows_dll_manager.py
+- https://github.com/Simple-Robotics/proxsuite-nlp/blob/main/bindings/python/proxsuite_nlp/__init__.py
+
+On windows, since Python 3.8, dll directories must be explicetly specified (cannot go through path), see
+- https://docs.python.org/3/library/os.html#os.add_dll_directory
+
+'''
+
+
+import os
+import sys
+import contextlib
+
+
+def get_dll_paths():
+    # Assumes that we are in a conda environment, and that ViSP DLLs and the dependencies are installed in this environment
+    # For the choice of defaults: see https://peps.python.org/pep-0250/#implementation
+    DEFAULT_DLL_PATHS = [
+      '..\\..\\..\\..\\bin', # when current folder is lib/python-version/site-packages/package
+      '..\\..\\..\\bin', # when current folder is lib/site-packages/package
+    ]
+    # If we have a different setup, the user should specify their own paths
+    visp_user_defined_dll_paths = os.getenv("VISP_WINDOWS_DLL_PATH")
+    if visp_user_defined_dll_paths is None:
+        return [
+            os.path.join(os.path.dirname(__file__), dll_path) for dll_path in DEFAULT_DLL_PATHS
+        ]
+    else:
+        return visp_user_defined_dll_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: # Below 3.8, the path variable is used to search for DLLs
+        return PathManager()