Detecting application start up with python

I've working on a windows python program and I need it to run once I open an app. Is it possible ? If so how would I implement it ?

We need some information, what did you want to do? Did you wanna know, if a process is started and then you will continue you python script? Than you can do this:

import psutil

def is_process_running(processName):
    for process in psutil.process_iter(): # iterates through all processes from your OS
        try: 
            if processName.lower() in process.name().lower(): # lowers the name, because "programm" != proGramm"
                return True # if the process is found, then return true
        except (psutil.NoSuchProcess, psutil.AccessDenied, psutil.ZombieProcess): # some failures what could go wrong
            pass
    return False;

while(!is_process_running('nameOfTheProcess') # only continue as long as the return is False
    time.sleep(10) # wait 10 seconds

For further information: psutil-docs