code: def mpixel(self, z, n=0):
          
          z = z * z + self.c
          if (abs(z) > 2.0):
              return self.color(n)
          n += 1
          if (n > self.max_iter):
              return None
          return self.mpixel(z, n)
docs: Iteration in Mandlebrot coordinate z.