random choice: how can I get a weighted presentation for x trials?

Question

I need a randomized selection of two values (300,-300) over x trials, I need both values to get selected at 50% of the time.

As an alternative I tried to create a list with both values presented there multiple times (5 x "300", 5 x "-300") and then shuffle the list each time and loop over it. I can not do that because of the current structure of the code and other resulting problems. I am new to python, too.

def one_stim_testing():
    facestims = choice(["-300", "300"])
    punktestims = choice(["-300", "300"])
    visual.ImageStim(win, "emo" + str(choice(range(23))) + ".jpg",
                     size=(300, 300), pos=(facestims,0)).draw()
    if facestims is "300": 
        visual.ImageStim(win, "neutral" + str(choice(range(23))) + ".jpg",size=(300, 300), pos=(-300,0)).draw()
    else:
        visual.ImageStim(win, "neutral" + str(choice(range(23))) + ".jpg", size=(300, 300), pos=(300,0)).draw()
    win.flip()
    core.wait(.5)
    win.flip()
    visual.ImageStim(win, "vertical.jpg",
                     size=(300,300), pos=(punktestims,0)).draw()
    if punktestims is "300":
        visual.ImageStim(win, "horizontal.jpg",
                         size=(300, 300), pos=(-300,0)).draw()
    else:
        visual.ImageStim(win, "horizontal.jpg",
                         size=(300, 300), pos=(300,0)).draw()

Answer 1

Do something like this:

    # Set up stimulus container once. Saves memory and ressources.
    # Do not generate new during runtime.
    image1 = visual.ImageStim(win, size=(300, 300))
    image2 = visual.ImageStim(win, size=(300, 300))

    image_horizontal = visual.ImageStim(win, image='horizontal.jpg', size=(300, 300))
    image_vertical = visual.ImageStim(win, image='vertical.jpg', size=(300, 300))

    # Generate factorial sequences
    # This is a list of dictionaries
    # There are better ways to do it in this particular example, 
    # but this approach scales well to all sorts of trial structures.
    REPETITIONS = 5
    trials = []
    for facestim in [-300, 300]:  # For each of these coordinates
        for punktestim in [-300, 300]:  # ... and for each of these coordinates
            for _ in range(REPETITIONS):  # ... and for each repetition:
                trials.append({'facestim': facestim,
                               'punktestim': punktestim})  #... add this combination

    # Randomize order
    random.shuffle(trials)
    #print(trials)  # If you want to inspect what happened

    # Showtime! Now loop through the factorial trials:
    for trial in trials:
        # Set image 1
        image1.image = 'emo%i.jpg' %choice(range(23))
        image1.pos = (trial['facestim'], 0)
        image1.draw()

        # Draw image 2 (the opposite side)
        image2.image = 'neutral%i.jpg' %choice(range(23))
        image2.pos = (-trial['facestim'], 0)  # The other coordinate
        image2.draw()

        # Show it
        win.flip()
        core.wait(0.5)
        win.flip()

        # Show horizontal and vertical in the correct positions
        image_vertical.pos = (trial['punktestim'], 0)
        image_vertical.draw()
        image_horizontal.pos = (-trial['punktestim'], 0)  # The other side
        image_horizontal.draw()

        # Perhaps a win.flip() here?

(code not tested because I don't have the stimuli)