How to keep the enemies inside the screen in pygame?

I want to keep the enemies (red rectangles in my case) inside the rectangle.What happens is that since it's a random function , the enemies keep on moving.But slowly some of my enemies moves outside , i don't want this to happen.I want them to be inside the screen only.

Here is my random movement for my enemies:

def evilMove(evilGuy):
    evilCoords = []
    #Returns either -1, 0 or 1
    randomMovex=random.randrange(-1,2)
    randomMovey=random.randrange(-1,2)
    evilMake={'x':evilGuy[0]['x']+randomMovex,'y':evilGuy[0]['y']+randomMovey}


    del evilGuy[-1] #Delete the previous spawn of enemy so there is no trail
    evilCoords.append(evilMake['x']) #Adds x coordinate
    evilCoords.append(evilMake['y']) #Adds y coordinate
    deadZones.append(evilCoords) #Adds the enemy coordinates in the list

    evilGuy.insert(0,evilMake)