linux python - can a program call itself?

Question

I have a python program that runs a cell model continuously. when I press "A" or "B" certain functions are called - cell divide, etc. when the "esc" key is pressed the simulation exits. Is there a way for the program to exit and then restart itself when "esc" is pressed?

Answer 1

The obvious solution is for the program to start a new copy of itself as the last thing it does before exiting. But you probably should think more along the lines of coding the simulator so that it can be reset without requiring a complete restart of the program.

Answer 2

Yes. This is probably what you want

The-Evil-MacBook:~ ivucica$ cat test.py
#!/usr/bin/env python
import sys
import os
print sys.argv[0] + " with argcount " + str(len(sys.argv))
if len(sys.argv) < 2 or sys.argv[1] != "2":
    print "doing recursion"
    os.system(sys.argv[0] + " 2");
else:
    print "not doing recursion"

exit(0)
The-Evil-MacBook:~ ivucica$ ./test.py
./test.py with argcount 1
doing recursion
./test.py with argcount 2
not doing recursion
The-Evil-MacBook:~ ivucica$ 

So when you want the program to restart itself, just call its sys.argv[0] using os.system() and immediately call exit(some_return_code_here) (zero means 'no error'). You might want to pass an extra argument so it knows it's a restarted instance, but are by no means required to do so; I did so above to prevent endless loop. If you have other mechanisms to prevent endless loops, then use those.

Please also note: for the above code, you need to run the program directly; python test.py did not do the trick for me (for obvious reasons). Also, above will probably work only under UNIX systems.

Note, also, that system() is blocking. If you need the original program to complete shutdown upon launching new program, easiest way would be to send the new one into background (thus "unblocking" system()). Just modify the line like this:

    os.system(sys.argv[0] + " 2 &");

Note the "&" which tells the shell to send the new process into background.