Assignment 3-Columbia life

150 students randomly go to school everyday from different streets.

def setup():
    size(500, 500)
    smooth()
    global columbia, student, population, speed, imagesize, x, xSpeed, y, ySpeed
    population=150
    imagesize = 10
    columbia = loadImage("columbia.png")
    student = loadImage("student.png")
    x = []
    y = []
    xSpeed = []
    ySpeed = []
    for i in range(population):
       x.append(random(0,500))
       y.append(random(0,500))
       xSpeed.append(random(-5,5))
       ySpeed.append(random(-5,5))
def draw():
    background(0)
    image(columbia,0,0,500,500)
    for i in range(population):
        x[i] = x[i] + xSpeed[i]
        y[i] = y[i] + ySpeed[i]        
        if (x[i] > width - imagesize) or (x[i] < imagesize):
            xSpeed[i] = xSpeed[i] * -1
        if (y[i] > height - imagesize) or (y[i] < imagesize):
            ySpeed[i] = ySpeed[i] * -1   
        noStroke()
        image(student,x[i],y[i],imagesize,imagesize)