虚拟环境中的 Python 依赖项导致 ROS2 colcon 构建失败并出现 ModuleNotFoundError

Question

当尝试构建我的 ROS2 项目时，由于缺少名为

ModuleNotFoundError

的依赖项，我在编译其中一个 C 模块时得到了

em

：

% colcon build --cmake-clean-cache
Starting >>> r1_messages
--- stderr: r1_messages                                                                     
CMake Error at /Users/mryall/src/mawson/ros2-iron-build/install/share/rosidl_adapter/cmake/rosidl_adapt_interfaces.cmake:57 (message):
  
  execute_process(/opt/homebrew/Frameworks/Python.framework/Versions/3.12/bin/python3.12
  -m rosidl_adapter --package-name r1_messages --arguments-file
  /Users/mryall/src/mawson/r1-ros/build/r1_messages/rosidl_adapter__arguments__r1_messages.json
  --output-dir
  /Users/mryall/src/mawson/r1-ros/build/r1_messages/rosidl_adapter/r1_messages
  --output-file
  /Users/mryall/src/mawson/r1-ros/build/r1_messages/rosidl_adapter/r1_messages.idls)
  returned error code 1:

  Traceback (most recent call last):

    File "<frozen runpy>", line 198, in _run_module_as_main
    File "<frozen runpy>", line 88, in _run_code
    File "/Users/mryall/src/mawson/ros2-iron-build/install/lib/python3.11/site-packages/rosidl_adapter/__main__.py", line 19, in <module>
      sys.exit(main())
               ^^^^^^
    File "/Users/mryall/src/mawson/ros2-iron-build/install/lib/python3.11/site-packages/rosidl_adapter/main.py", line 53, in main
      abs_idl_file = convert_to_idl(
                     ^^^^^^^^^^^^^^^
    File "/Users/mryall/src/mawson/ros2-iron-build/install/lib/python3.11/site-packages/rosidl_adapter/__init__.py", line 18, in convert_to_idl
      from rosidl_adapter.msg import convert_msg_to_idl
    File "/Users/mryall/src/mawson/ros2-iron-build/install/lib/python3.11/site-packages/rosidl_adapter/msg/__init__.py", line 16, in <module>
      from rosidl_adapter.resource import expand_template
    File "/Users/mryall/src/mawson/ros2-iron-build/install/lib/python3.11/site-packages/rosidl_adapter/resource/__init__.py", line 19, in <module>
      import em

  ModuleNotFoundError: No module named 'em'

Call Stack (most recent call first):
  /Users/mryall/src/mawson/ros2-iron-build/install/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:132 (rosidl_adapt_interfaces)
  CMakeLists.txt:14 (rosidl_generate_interfaces)

---
Failed   <<< r1_messages [4.13s, exited with code 1]

我的 ROS2 安装是使用 Python 虚拟环境构建的，我已激活该环境。但是，即使激活了 virtual-env 并且使用

pip

安装了所有必需的库，但使用 CMake 构建的 ROS 模块似乎无法找到它。

我尝试检查

em

库是否已安装。运行

pip install empy

确认已安装：

% pip install empy
Requirement already satisfied: empy in /Users/mryall/src/mawson/ros2-iron/iron_venv/lib/python3.11/site-packages (3.3.4)

Answer 1

ROS2 中的 CMake 模块不会自动选取调用

colcon

的 shell 使用的虚拟环境。 （这显然是 ROS2 维护者有意为之的决定，他们似乎不太了解虚拟环境的目的或操作。）

您可以通过要求

colcon

将

Python3_EXECUTABLE

参数传递给 CMake 来修复此问题，并使用 shell 中的

$VIRTUAL_ENV

环境变量和活动的 virtualenv：

% colcon build --cmake-args -DPython3_EXECUTABLE="$VIRTUAL_ENV/bin/python"

幸运的是，一旦知道了正确的二进制文件，Python 就足够聪明，可以找到安装在 virtualenv 中的库。

这使得 ROS2 代码中的 C++/CMake 模块能够找到其所有 Python 依赖项。