Add support for ament_cmake_python in ros2 pkg create

[RFRIEDM-Trimble]

Feature request

Feature description

ROS2 CLI allows creating packages for cmake, ament_cmake, ament_python. Considering there isn't a complete example in the documentation for ament_cmake_python , it would be helpful to support generating one for users.

Implementation considerations

Follow best practices for using ament.
Supply a working example with both C++ and python code.
Ensure dependencies are exported correctly.

[bismuth01]

I have a few questions regarding the issue in my attempt to solve it: -

• Do I strictly follow the folder structure in the documentation as it seems having include and src directory like in ament_cmake might be better.
• Is it only for the rolling branch ?
• Any other suggestions or coding style or best practices I have to adhere to ?

[christophebedard]

Someone attempted this before; you should take a look at the PR and the discussion: #904.

And yes, you should target the rolling branch, and we can consider backporting it to other branches afterwards.

[bismuth01]

I read the discussion, so to solve the issue, rather than implement a separate ament_cmake_python package type, a template type of python must be implemented with build type ament_cmake.

So, what are the new requirements to solve the issue and is it still open ?

[christophebedard]

I think that's about it! It should still use --build-type ament_cmake because a package using ament_cmake_python is still a package of build type ament_cmake: ament_cmake_python is just a set of CMake utilities for ament_cmake packages that contain Python code. We just want to use a different template file, and we'd like for it to be selected using --template-name python (+ --build-type ament_cmake).

In summary:

1. --build-type ament_cmake: uses the current template
2. --build-type ament_cmake --template-name cmake: uses the current template too (we assume that --template-name cmake is the default with --build-type ament_cmake)
3. --build-type ament_cmake --template-name python: uses a new template for ament_cmake packages that contain Python code and thus use ament_cmake_python, like the one in Support ament_cmake_python for pkg create #904

This hasn't been implemented as far as I can tell, so yes this is still open!

[bismuth01]

Sorry, got caught up in the college semester, now I am working on this issue. I would like to ask that if ament_cmake_python is no longer a build type, then how will the package.xml and CMakeLists.txt change ? Already did rest of the changes to create directory and generate rest of the files.
The documentation does not clarify that part.

Also, what happens to the build-type cmake. Build types ament_cmake and cmake output different projects. So as per your points above, cmake build type should be removed.

[vinayak1729-web]

Hi @bismuth01, @christophebedard,

I’m interested in contributing to the ament_cmake_python support for ros2 pkg create (#739). I noticed the recent discussion about using --template-name python with --build-type ament_cmake and the need for updated package.xml and CMakeLists.txt templates. Could you confirm if the issue is still open for contributions? If so, I’d like to work on implementing the Python template and testing it with a sample package containing both C++ and Python nodes.

For clarification, should the new template include a specific folder structure (e.g., scripts/ for Python executables and <package_name>/ for modules)? Also, are there any additional best practices or test requirements I should follow beyond what’s outlined in the ROS2 contribution guidelines?

Looking forward to your guidance!

Thanks,
Vinayak Shinde

[christophebedard]

@vinayak1729-web I'm happy to see that you want to contribute! However, someone is already working on this issue. Please take a look at some other help wanted/good first issue issues that someone hasn't already claimed.

[christophebedard]

Sorry, got caught up in the college semester, now I am working on this issue. I would like to ask that if ament_cmake_python is no longer a build type, then how will the package.xml and CMakeLists.txt change ? Already did rest of the changes to create directory and generate rest of the files. The documentation does not clarify that part.

Also, what happens to the build-type cmake. Build types ament_cmake and cmake output different projects. So as per your points above, cmake build type should be removed.

@bismuth01 sorry for the late reply.

I am talking about the ament_cmake build type here, not the cmake build type. The cmake build type can be left as-is.

There is currently only one "version" of the template files used for the ament_cmake build type. What we want to do here is to have another version of the template files that uses ament_cmake_python, similar to what's described in the docs.

In my comment above (#739 (comment)), I proposed to select the version of the template files using a new --template-name option, which could only be used with --build-type ament_cmake, since it only applies to the ament_cmake build type:

1. --build-type ament_cmake: uses the current template
2. --build-type ament_cmake --template-name cmake: uses the current template too (we assume that --template-name cmake is the default with --build-type ament_cmake)
3. --build-type ament_cmake --template-name python: uses a new template for ament_cmake packages that contain Python code and thus use ament_cmake_python, like the one in Support ament_cmake_python for pkg create #904

The files for the two different versions (1&2 vs 3 above) are almost the same, except for these extra lines in the template files used when we select --template-name python:

1. CMakeLists.txt:
   1. Add find_package(ament_cmake_python REQUIRED) at the top, as shown here
   2. Add ament_python_install_package(${PROJECT_NAME}) before the tests, as shown here
   3. Add some code for Python tests inside if(BUILD_TESTING) ... endif(), as shown here
2. package.xml:
   1. Add a buildtool_depend on ament_cmake_python, as shown here
   2. Add a test_depend on ament_cmake_pytest, as shown here

Does that help? Since the files are almost the same, you could have one set of template files and only include the ament_cmake_python parts I described above using some @[if ...]@ conditions in the .em template file if the user selects --template-name python.

If you've already made some changes in a branch, you could create a PR and we can discuss there.

[bismuth01]

@christophebedard I am almost done with the changes, I just want to know on how to handle node name and library name ?
Do I take those arguments in consideration and if yes, then which kind should be generated (python or cmake) ?

[christophebedard]

Please open a PR. It can be a draft PR, and you can ask your questions there.