def mandel(x, y, max_iters):
    """
      Given the real and imaginary parts of a complex number,
      determine if it is a candidate for membership in the Mandelbrot
      set given a fixed number of iterations.
    """
    c = complex(x, y)
    z = 0.0j
    for i in range(max_iters):
      z = z*z + c
      if (z.real*z.real + z.imag*z.imag) >= 4:
        return i, z

    return max_iters, z