How to attach a function to a class

In "Presenting stimulus for fixed duration" we saw how we can easily write a new class to extend existing classes with new functions. While it works, I always had the problem to put this class on every computer and to have it work correctly with different Python Path settings. So, here is a neat trick how to do the same without writing your own class:

from pyepl.locals import *

def present_fixed_dur(clk=None, duration=None, bc=None, minDuration=None):

        """

        This is just like the standard Image.present, except

        that if you press a button, the image stays on the

        screen until the full duration has passed.



        I got rid of the jitter argument, because it makes

        things complicated.

        """



        v = VideoTrack.lastInstance()

        

        # get the clock if needed

        if clk is None: clk = PresentationClock()



        # show the image

        t = v.showCentered(self)

        timestamp = v.updateScreen(clk)



        if bc:

            # wait for button press

            button,bc_time = bc.waitWithTime(minDuration,duration,clk)

            # figure out how much time is remaining, now

            # that they've pressed the button, and delay for

            # just that

            rt = bc_time[0] - timestamp[0]

            clk.delay(duration-rt)

        else:

            clk.delay(duration)



        # unshow that image

        v.unshow(t)

        upd_ts = v.updateScreen(clk)

        # print 'presented for %ims' % (upd_ts[0] - timestamp[0])



        if bc: return timestamp,button,bc_time

        else: return timestamp



# Use a reference to the function and attach it as a attribute to the Image class

Image.present_fixed_dur = present_fixed_dur

Et voila, we extended the Image class on the fly. :)