Python Koans Solution —— None

Python Koans是一个学习Python编程语言的交互式教程，通过解决当中的问题来更深刻地理解Python。本系列文章为在此项目的学习中的问题解决方案及思考
Github Address: Python Koans Download Address

Lesson 3 None

None是一个特殊的常量，有自己的数据类型NoneType。None和任何其他的数据类型比较永远返回False。可以将None复制给任何变量，但是不能创建其他NoneType对象。

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about_none.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from runner.koan import *

class AboutNone(Koan):

    def test_none_is_an_object(self):
        "Unlike NULL in a lot of languages"
        self.assertEqual(True, isinstance(None, object))

    def test_none_is_universal(self):
        "There is only one None"
        self.assertEqual(True, None is None)

    def test_what_exception_do_you_get_when_calling_nonexistent_methods(self):
        """
        What is the Exception that is thrown when you call a method that does
        not exist?

        Hint: launch python command console and try the code in the block below.

        Don't worry about what 'try' and 'except' do, we'll talk about this later
        """
        try:
            None.some_method_none_does_not_know_about()
        except Exception as ex:
            ex2 = ex

        # What exception has been caught?
        #
        # Need a recap on how to evaluate __class__ attributes?
        #
        #     http://bit.ly/__class__

        self.assertEqual(AttributeError, ex2.__class__)

        # What message was attached to the exception?
        # (HINT: replace __ with part of the error message.)
        self.assertRegex(ex2.args[0], "\'NoneType\' object has no attribute \'some_method_none_does_not_know_about\'")

    def test_none_is_distinct(self):
        """
        None is distinct from other things which are False.
        """
        self.assertEqual(True, None is not 0)
        self.assertEqual(True, None is not False)