python challenge level 2

level 2 的链接如下：

从题目的图中看不出什么，但是有这么一句话：

recognize the characters. maybe they are in the book, but MAYBE they are in the page source.

识别字母，可能是在页面源码中

我们来看一下页面源码中有这么一句话：

find rare characters in the mess below

意思是找个下面所有字符中的字母，把这些字符保存到mess.txt，然后用python写个程序找到其中的字符，代码如下：

#!/usr/bin/env python3

def get_charaters(line):
    chars = ""
    for c in line:
        if 'a' <= c <= 'z':
            chars += c
    return chars

try:
    with open("mess.txt") as file:
        for line in file:
            str = get_charaters(line)
            print(str, end = '')
except IOError as err:
    print(err)

运行一下，得到的结果是：

equality

在浏览器中输入http://www.pythonchallenge.com/pc/def/equality.html，果然进入了level 3