If you want this to happen by default when you run screen, then you'll need to edit your .screenrc file. You can use the chdir directive to have a new screen window change directories upon opening it, but you'll want to explicitly reset that after your needs are met, so that newer windows are not affected.
# .screenrc settings to cd to repos and run python-script.py
screen -t "Python Script" ./python-script.py
# reset the default directory for new windows.
screen -t "New Window" bash
screen -t "SSH Session" ssh firstname.lastname@example.org
Keep in mind that this will essentially set "./python-script.py" as the shell for that window, so when python-script.py is finished the window will close.