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5.12: Epoch Time

  • Page ID
    14542
  • Also in order to "time out", the current time (returned by time.time()) minus four seconds (because 4 is stored in TIMEOUT) must be greater than the last time clicked a button (stored in lastClickTime). The reason why time.time() - TIMEOUT > lastClickTime works has to do with how epoch time works. Epoch time (also called Unix epoch time) is the number of seconds it has been since January 1st, 1970. This date is called the Unix epoch.

    For example, when I run time.time() from the interactive shell (don’t forget to import the time module first), it looks like this:

    >>> import time
    >>> time.time()
    1320460242.118 
    

    What this number means is that the moment the time.time() function was called was a little over 1,320,460,242 seconds since midnight of January 1st, 1970. (This translates to November 4th, 2011 at 7:30:42pm. You can learn how to convert from Unix epoch time to regular English time at http://invpy.com/epochtime)

    If I call time.time() from the interactive shell a few seconds later, it might look like this:

    >>> time.time()
    1320460261.315
    

    1320460261.315 seconds after midnight of the Unix epoch is November 4th, 2011 at 7:31:01pm. (Actually, it’s 7:31 and 0.315 seconds if you want to be precise.)

    Dealing with time would be difficult if we had to deal with strings. It’s hard to tell that 19 seconds have passed if we only had the string values '7:30:42 PM' and '7:31:01 PM' to compare. But with epoch time, it’s just a matter of subtracting the integers 1320460261.315 - 1320460242.118, which evaluates to 19.197000026702881. This value is the number of seconds between those two times. (The extra 0.000026702881 comes from very small rounding errors that happen when you do math with floating point numbers. They only happen sometimes and are usually too tiny to matter. You can learn more about floating point rounding errors at http://invpy.com/roundingerrors.)

    Going back to line 121, if time.time() - TIMEOUT > lastClickTime evaluates to True, then it has been longer than 4 seconds since time.time() was called and stored in lastClickTime. If it evaluates to False, then it has been less than 4 seconds.

                    # pushed the incorrect button, or has timed out
                    gameOverAnimation()
                    # reset the variables for a new game:
                    pattern = []
                    currentStep = 0
                    waitingForInput = False
                    score = 0
                    pygame.time.wait(1000)
                    changeBackgroundAnimation()
    

    If either the player clicked on the wrong button or has timed out, the program should play the "game over" animation and then reset the variables for a new game. This involves setting the pattern list to a blank list, currentStep to 0, waitingForInput to False, and then score to 0. A small pause and a new background color will be set to indicate to the player the start of a new game, which will begin on the next iteration of the game loop.