#!/usr/bin/env python3
 
from PIL import Image, ImageDraw
from functools import reduce
 
# ニュートン法はfunctools.reduceを使った方がシンプルに書ける
def newton(x):
    return reduce(lambda j, i: j - (j**3 - 1) / (3 * j**2), range(10), x)
 
def plot(draw, s):
    tpl = (255, 0, 0)
    # 右辺のtplの「回転結果」のリスト要素は左辺に「構造化代入」される
    red, green, blue = [tpl[i:] + tpl[:i] for i in range(3, 0, -1)]
    # ローカル関数fooを定義する
    def foo(x, y):
        # Pythonはマトモなスコープが無いので、ローカル関数から数値等の単項データ
        # (この場合はs)を参照出来ないので、nonlocal宣言を使う
        nonlocal s
        # hs の定義はローカル関数内にあった方がいい(ここ以外では使われていない)
        hs = s // 2
        z = newton(complex(x - hs + 0.5, -y + hs + 0.5) / s * 4)
        # 条件分岐「文」ではなく、条件分岐「式」に慣れよう
        return red if z.real > 0 else \
               green if z.real < 0 and z.imag > 0 else \
               blue
    # Pythonではfor文を使うよりリスト内包表記を使った方がスマートだ
    [draw.rectangle([x, y, x + 1, y + 1], fill = foo(x, y)) \
     for y in range(s) for x in range(s)]
 
# スクリプトとして起動する
if __name__ == '__main__':
    size = 512
    img = Image.new('RGB', (size, size))
    plot(ImageDraw.Draw(img), size)
    img.show()
    img.save('img.png')
 

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