Add solution to mission 31

Author: scorphus

31-grandpa.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+# This file is part of Python Challenge Solutions
+# https://github.com/scorphus/PythonChallengeSolutions
+
+# Licensed under the BSD-3-Clause license:
+# https://opensource.org/licenses/BSD-3-Clause
+# Copyright (c) 2018-2020, Pablo S. Blum de Aguiar <scorphus@gmail.com>
+
+# http://www.pythonchallenge.com/pc/rock/grandpa.html
+
+from auth import get_last_attr
+from auth import get_last_src_url
+from auth import read_url
+from cache import autocached
+from etc import factorize
+from etc import image_to_text
+from io import BytesIO
+from PIL import Image
+
+
+def convert_to_number(s):
+    try:
+        return int(s)
+    except ValueError:
+        return float(s)
+
+
+def read_riddle_numbers(url):
+    for el in ["left", "top", "width", "height", "iterations"]:
+        yield convert_to_number(get_last_attr(url, el))
+
+
+def read_riddle_data(url):
+    img_url = get_last_src_url(url)
+    return (Image.open(BytesIO(read_url(img_url))), *read_riddle_numbers(url))
+
+
+@autocached
+def mandelbrot_set(left, top, width, height, image_size, max_iter):
+    """Generates an upside-down section of the Mandelbrot Set as pixel data for
+    an image of size `image_size` doing `max_iter` maximum iterations"""
+    dx = width / image_size[0]
+    dy = height / image_size[1]
+    data = []
+    for y in range(image_size[1] - 1, -1, -1):  # is mission's image upside down??? 🤷
+        for x in range(image_size[0]):
+            c0 = complex(left + x * dx, top + y * dy)
+            c, i = complex(), 0
+            while True:
+                c = c * c + c0
+                if abs(c) > 2 or i == max_iter - 1:
+                    break
+                i += 1
+            data.append(i)
+    return data
+
+
+def diff_image(data_a, data_b):
+    """Generates a 1-bit black and white image by comparing `data_a` and `data_b`"""
+    diff = [int(a > b) for a, b in zip(data_a, data_b) if a != b]
+    img = Image.new("1", factorize(len(diff)))
+    img.putdata(diff)
+    return img
+
+
+url = "http://www.pythonchallenge.com/pc/rock/grandpa.html"
+img, left, top, width, height, iterations = read_riddle_data(url)
+mandelbrot = mandelbrot_set(left, top, width, height, img.size, iterations)
+diff_img = diff_image(img.getdata(), mandelbrot)
+print(image_to_text(diff_img, skip=1, white="▓▓"))

auth.py

@@ -19,6 +19,7 @@
     "http://www.pythonchallenge.com/pc/return": b"huge:file",
     "http://www.pythonchallenge.com/pc/hex": b"butter:fly",
     "http://www.pythonchallenge.com/pc/ring": b"repeat:switch",
+    "http://www.pythonchallenge.com/pc/rock": b"kohsamui:thailand",
 }
 
 
@@ -49,10 +50,15 @@ def read_riddle(url, headers={}):
     return read_url(url, headers).decode()
 
 
+def get_last_attr(url, attr):
+    """Extracts the URL of the last `attr` attribute in the mission at `url`"""
+    return read_riddle(url).split(f'{attr}="')[-1].split('"')[0]
+
+
 def get_last_attr_url(url, attr):
     """Extracts the URL of the last `attr` attribute in the mission at `url`"""
-    img_src = read_riddle(url).split(f'{attr}="')[-1].split('"')[0]
-    return "{}/{}".format(url.rsplit("/", 1)[0], img_src)
+    attr = get_last_attr(url, attr)
+    return "{}/{}".format(url.rsplit("/", 1)[0], attr)
 
 
 def get_last_src_url(url):