This python function checks whether a file exists. If not, the function waits for a user specified time and checks again. As soon as the file appears, a reaction can be specified. A log is written while the function runs to inform the user about the current status.

check_file.py

def check_output(file, interval_time, logfile_path):
    import os
    import time

    status = os.path.isfile(file)


    while status is not True:
        f_log = open(logfile_path, 'a')
        f_log.write(time.asctime() + '\t' + 'Still running\n')
        f_log.close()
        time.sleep(interval_time)
        status = os.path.isfile(file)


    # What should be done after the file appears?
    # This goes here:


    f_log = open(logfile_path, 'a')
    f_log.write(time.asctime() + '\t' + 'FINISHED\n')
    f_log.close()