Example:
subprocess.Popen(‘subl.exe’, ‘Packages\User\Project\Autohotkey.sublime-project’])

This open in new window instead of switching current view.
How to switch to that project in the same view?

We ran into something similar with building projects for our plugin. Sublime will load a project in a new window if there is an active project or open files. I believe our solution was to close the active project and open files and then run the command to open sublime with the specific project.

window.run_command("close_project") # close the project
window.run_command("close_all") #close all active files

I hope this helps!

-Nick