Unit 1, Mandelbrot (Python, v3)

# Limit for maximum iterations
MAX_ITER = 256
SYMBOLS = ".:coCO8@"


height = input("Enter size of the fractal (height and width)\n")
width = input()

def c(x, y):
    x0 = (3.5 / width) * x - 2.5
    y0 = (2.0 / height) * y - 1
    xi = yi = iteration = 0

    while xi**2 + yi**2 < 4 and iteration < MAX_ITER:
        xtemp = xi**2 - yi**2 + x0
        yi = 2*xi*yi + y0
        xi = xtemp
        iteration += 1

    if (iteration == MAX_ITER):
        return " "
    return SYMBOLS[(iteration - 1) % 8]

for y in range(height):
    print "".join([c(x, y) for x in range(width)])