Fix python controllers on Windows (cyberbotics#6933)

* Fix python controllers on Windows

* Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Support from Python 3.8 only

* simplified

* Fix DLL directory handle retention in Python controller on Windows (cyberbotics#6934)

* Initial plan

* Store DLL directory handles to prevent garbage collection

Co-authored-by: omichel <1264964+omichel@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: omichel <1264964+omichel@users.noreply.github.com>

* Update changelog for R2025 with Python fix

Added entry for fixing Python controllers on Windows.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
Co-authored-by: omichel <1264964+omichel@users.noreply.github.com>

Author: 3 people

docs/guide/preferences.md

@@ -22,7 +22,7 @@ Note that this is the maximum number of threads allowed, but the actual number o
 - The **Python command** defines which Python command is invoked by Webots when starting a Python controller.
 The default value is `python`.
 It should work on most systems assuming that `python` is installed and available from the command line.
-On some systems, it may be useful to set it to `python3.7` for example if you want to launch the controllers with this specific version of Python.
+On some systems, it may be useful to set it to `python3.14` for example if you want to launch the controllers with this specific version of Python.
 Bear in mind that this value may be overridden by the content of a `runtime.ini` file of a Python controller that may redefine a specific Python command to launch that controller.
 - The **Extra project path** defines the paths to user folders similar to the `WEBOTS_HOME/projects` folder.
 These user folders should contain projects resources that can be used in the current project (such as PROTO nodes, controllers, textures, etc.).

docs/guide/using-python.md

@@ -8,7 +8,7 @@ The Python API is currently composed of a set of about 25 classes having about 2
 The classes are either representations of a node of the scene tree (such as Robot, LED, etc.) or utility classes (such as Motion, ImageRef, etc.).
 A complete description of these functions can be found in the reference guide while the instructions about the common way to program a Python controller can be found in [this chapter](programming-fundamentals.md).
 
-The Python API of Webots supports Python versions from 3.7.
+The Python API of Webots supports Python versions from 3.8.
 
 Alternatively to the Webots built-in editor, [PyCharm](https://www.jetbrains.com/pycharm) can be used to edit and launch Python controllers, see the [Using PyCharm with Webots](using-your-ide.md#pycharm) chapter for a step-by-step procedure.
 

docs/reference/changelog-r2025.md

@@ -22,6 +22,7 @@
     - Fixed a crash occurring when Python was not found on Windows ([#6870](https://github.com/cyberbotics/webots/pull/6870)).
     - Fixed detection of physics plugins in extra projects ([#6880](https://github.com/cyberbotics/webots/pull/6880)).
     - Fixed `addForceWithOffset` and `addTorque` doing the same thing as `addForce` in Python ([#6881](https://github.com/cyberbotics/webots/pull/6881)).
+    - Fixed Python controllers on Windows ([#6933](https://github.com/cyberbotics/webots/pull/6933)).
 
 ## Webots R2025a
 Released on January 31st, 2025.

lib/controller/python/controller/wb.py

@@ -16,10 +16,32 @@
 import os
 import sys
 
+# Keep DLL directory handles alive to prevent garbage collection (Windows only)
+_dll_directory_handles = []
+
 if sys.platform == 'linux' or sys.platform == 'linux2':
     path = os.path.join('lib', 'controller', 'libController.so')
 elif sys.platform == 'win32':
     path = os.path.join('lib', 'controller', 'Controller.dll')
+    # Since Python 3.8, dependent DLLs are no longer found via PATH on Windows.
+    # Add directories containing required runtime DLLs to the search path.
+    webots_home = os.environ['WEBOTS_HOME']
+    for dll_dir in [
+        os.path.join(webots_home, 'lib', 'controller'),
+        # In the installed distribution, MinGW runtime DLLs (libgcc_s_seh-1.dll,
+        # libwinpthread-1.dll, libstdc++-6.dll) are placed in msys64/mingw64/bin/cpp.
+        os.path.join(webots_home, 'msys64', 'mingw64', 'bin', 'cpp'),
+        os.path.join(webots_home, 'msys64', 'mingw64', 'bin'),
+    ]:
+        if os.path.isdir(dll_dir):
+            _dll_directory_handles.append(os.add_dll_directory(dll_dir))
+    # For development builds running from source, also check the system MSYS2 installation.
+    mingw_bin = os.path.join(os.environ.get('MSYS2_HOME',
+                             os.path.splitdrive(sys.executable)[0] + os.sep + 'msys64'),
+                             'mingw64',
+                             'bin')
+    if os.path.isdir(mingw_bin):
+        _dll_directory_handles.append(os.add_dll_directory(mingw_bin))
 elif sys.platform == 'darwin':
     path = os.path.join('Contents', 'lib', 'controller', 'libController.dylib')