文档测试

看到Python的官方文档，很多都有示例代码，比如re模块就带了很多示例代码：

>>> import re
>>> m = re.search('(?<=abc)def', 'abcdef')
>>> m.group(0)
'def'

可以把示例代码在Python的交互式环境下输入执行，结果与文档的示例代码显示的一致。

当我们编写注释，写上下面的注释更友好：

def abs(n):
    '''
    Function to get absolute value of number.

    Example:
    >>> abs(1)
    1
    >>> abs(-1)
    1
    >>>abs(0)
    0
    '''
    return  n if n >= 0 else (-n)

好处：

• 告诉函数的调用者该函数期望输入和输出
• Python内置的“文档测试”（doctest）模块可以直接提取注释中的代码并执行测试
• doctest 严格按照Python交互式命令行的输入和输出判断测试结果是否正确，只有测试异常的时候，可以用...表示一大推输出

使用doctest来测试编写的Dict类：

class Dict(dict):
    '''
    Simple dict but also support access as x.y style.

    >>> d1 = Dict()
    >>> d1['x'] = 100
    >>> d1.x
    100
    >>> d1.y = 200
    >>> d1['y']
    200
    >>> d2 = Dict(a=1, b=2, c='3')
    >>> d2.c
    '3'
    >>> d2['empty']
    Traceback (most recent call last):
        ...
    KeyError: 'empty'
    >>> d2.empty
    Traceback (most recent call last):
        ...
    AttributeError: 'Dict' object has no attribute 'empty'
    '''
    def __init__(self, **kw):
        super(Dict, self).__init__(**kw)

    def __getattr__(self, key):
        try:
            return self[key]
        except KeyError:
            raise AttributeError(r"'Dict' object has no attribute '%s'" % key)

    def __setattr__(self, key, value):
        self[key] = value

if __name__=='__main__':
    import doctest
    doctest.testmod()

运行后什么也没输出，这说明编写的doctest运行都是正确的， 如果程序有问题，比如我们试着把 __ getattr__ 注释掉，
会有就会有报错：

注释如下：

    # def __getattr__(self, key):
    #     try:
    #         return self[key]
    #     except KeyError:
    #         raise AttributeError(r"'Dict' object has no attribute '%s'" % key)

执行结果，报错内容：

Error
**********************************************************************
File "E:/pyplace/learn_python3/learn/two/测试/文档测试/mydict2.py", line 7, in Dict
Failed example:
    d1.x
Exception raised:
    Traceback (most recent call last):
      File "D:\JetBrains\PyCharm 2018.1.1\helpers\pycharm\docrunner.py", line 140, in __run
        compileflags, 1), test.globs)
      File "<doctest Dict[2]>", line 1, in <module>
        d1.x
    AttributeError: 'Dict' object has no attribute 'x'


Error
**********************************************************************
File "E:/pyplace/learn_python3/learn/two/测试/文档测试/mydict2.py", line 13, in Dict
Failed example:
    d2.c
Exception raised:
    Traceback (most recent call last):
      File "D:\JetBrains\PyCharm 2018.1.1\helpers\pycharm\docrunner.py", line 140, in __run
        compileflags, 1), test.globs)
      File "<doctest Dict[6]>", line 1, in <module>
        d2.c
    AttributeError: 'Dict' object has no attribute 'c'


Process finished with exit code 0

总结：

• Python 官方文档的示例代码，可以在Python 交互式环境下执行。
• 写注释会显得更加有好

github地址： https://github.com/shenshizhong/learn_python3