fix shebang line for python3

[mikaelarguedas]

Currently in Noetic/Focal the script cannot be run with rosrun:

/usr/bin/env: ‘python’: No such file or directory

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/ros-noetic-ninjemys-release/14262/22

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/poll-kinetic-users-kinetic-eol-in-april-what-is-your-migration-plan/17731/10

[sloretz]

I would recommend fixing by using catkin_install_python here instead of changing the shebang.

class_loader/CMakeLists.txt

Line 79 in 4a9ed1a

install(PROGRAMS scripts/class_loader_headers_update.py

Installing python-is-python3 might be another workaround.

[mikaelarguedas]

This is a noetic-devel branch.
Why is it recommended to use one of the other workarounds ? Is it to support non debian platforms ?

[sloretz]

Is it to support non debian platforms ?

Yeah, catkin_install_python() also does something for Windows.

https://github.com/ros/catkin/blob/a9672d78ec483c3a991a051c365da329fceaa9f2/cmake/catkin_install_python.cmake#L77-L82
https://github.com/ros/catkin/blob/a9672d78ec483c3a991a051c365da329fceaa9f2/cmake/platform/windows.cmake#L109-L123

[mikaelarguedas]

I remember now why I used catkin_install_python on most PRs but not this one. This CMake is made to be working even in an environment without catkin installed. So we can't catkin_install_python outside a if(catkin_FOUND) block. But that means duplicating the install directive in the 2 branches of that if and use install(PROGRAMS in the else case (although that means that on a linux without catkin the installed file won't have the right shebang line...) WDYT?

[mikaelarguedas]

@sloretz any feedback on the previous comment ?

[sloretz]

This CMake is made to be working even in an environment without catkin installed. So we can't catkin_install_python outside a if(catkin_FOUND) block. But that means duplicating the install directive in the 2 branches of that if and use install(PROGRAMS in the else case (although that means that on a linux without catkin the installed file won't have the right shebang line...) WDYT?

Hmm, the catkin_install_python() logic is a lot to reproduce in the non-catkin environment. Changing the shebang in the file won't work on Windows, but works for the non-catkin case on linux. Changing the install rule to catkin_install_python when catkin is found will work on windows, but won't help the non-catkin case.

I would lean towards using catkin_install_python if catkin is found and requiring non-catkin workflows to install python-is-python3 on Debian platforms, but a decision on what non-required platforms should be better supported is one the maintainer should make. @nuclearsandwich thoughts?

[hidmic]

I would lean towards using catkin_install_python if catkin is found and requiring non-catkin workflows to install python-is-python3 on Debian platforms, but a decision on what non-required platforms should be better supported is one the maintainer should make. @nuclearsandwich thoughts?

This is a sound path forward. @nuclearsandwich ?

[sloretz]

Thank you for the PR!