A Processing program that draws a "clock" diagram with concentric rings of integers. Mayb be useful for teaching modular arithmetic to students

modular_arithmetic_clock.pyde

"""
Processing 3, with Python 3.
Draws a circle containing 4 concentric rings of numbers, increasing as they move inwards,
so the first ring shows, for draw_clock(12), [0, 11], the second ring shows [12, 24], etc.
This is useful for generating diagrams to help explain modular arithmetic to students.
Think of it like a clock face,and you "wrap around" when you reach the top again.
"""

def to_cart(r, theta):
    return (width/2 + r*cos(radians(theta)), width/2 - r*sin(radians(theta)))

def num_ring(n1, n2, r):
    fill(0)
    for (i,j) in zip(range(n1,n2), range(450, 90, -(360/(n2 - n1)))):
        (x, y) = to_cart(r, j)
        text(i, x, y)

def draw_clock(n):
    size(512, 512)
    background(255)
    fill(255)
    ellipse(width/2, width/2, width, width)
    rs = map(lambda x: x/10.0 * width/2, range(8, -2, -2))
    for (i,r) in zip(range(n, 5*n, n), rs):
        num_ring(i - n, i, r)

draw_clock(12)