filename=pickAFile()
pic=makePicture(filename)
show(pic)
w = getWidth(pic)
h = getHeight(pic)
col=1
while col<w:
    row=1
    while row<h:
        pixel = getPixel(pic,col,row)
        setColor(pixel,green)
        row=row+4
    col=col+1
repaint(pic)

conditional interest:

principal=input('please enter the principal:')
years = input('please enter the number of years')


i=0
while i<years:
    if i>3:
        rate=.3
    if principal<10000:
        rate=.1
    elif principal>=10000:
        rate=.2
    if principal>50000:
        rate=.25
    if years>3:
        rate=.3 
    interest=principal*rate
    principal=principal+interest
    i=i+1

print principal