Write out only first result in while loop in psychopy

Question

I want to print my trial onset time to my logfile. However, I need to write to the logfile within a while (timer) loop, which means what whatever I do in that loop will be done for every screen refresh.

The problem is that I only want to write the result of the first clock.getTime() call to the logfile. If I do this:

while timer.getTime() >0: # while time isn't up (turns neg when time's up)
    for key in event.getKeys():
        if key in ['escape']:
            core.quit() # quit if they press escape

        timeText.draw(window)
        timeline.draw(window)
        cursorImage.draw(window)

        ## flip so it actually appears
        window.flip()
        OnsetTime = clock.getTime()
        logfile.write('OnsetTime, %s' % OnsetTime)

I get a bunch of lines of my logfile that say 'OnsetTime' and the time - one for every refresh.

I only want the first one to be printed, but I'm not sure how to do that.

Answer 1

This is just another way of doing what CasualDemon's proposing, but one which I think is more elegant (three lines of code for the logging instead of 5):

def logOnsetTime():
    """Function which allows launching this code right after a window.flip()"""
    logfile.write('OnsetTime, %s' % clock.getTime())

window.callOnFlip(logOnsetTime)  # runs on first flip
while timer.getTime() >0: # while time isn't up (turns neg when time's up)
    for key in event.getKeys():
        if key in ['escape']:
            core.quit() # quit if they press escape

        timeText.draw(window)
        timeline.draw(window)
        cursorImage.draw(window)

        ## flip so it actually appears.
        window.flip()

If you want a log for every keypress, put the window.callOnFlip(logOnsetTime) inside the while loop. There's also a window.logOnFlip method specifically for logging, but that just saves an input string to the log, timestamped to a global clock, so it wouldn't save the time of your clock.