Exit code 127 means that the child process cannot find the command.
So if you run a python script from an exec node, in the python script there is probably a call to some command that does not have an absolute path and if that command is not in the default PATH variable, you will get an exit code 127.
On commandline type which qr and use that output in the exec node.
If qr is a python script, you can either edit that script or modify the PATH variable to make it available (check the variable with env | grep PATH - if the command located in the shown directories, then it is a different issue)
