默认实现

如果我们没有实现两个方法的任何一个，会打印出什么呢？

import logging

logging.basicConfig(level=logging.INFO,

format='%(asctime)s - [line:%(lineno)d] - %(levelname)s: %(message)s')

class TechlogTest:

# def __str__(self):

# return "TechlogTest.__str__"

#

# def __repr__(self):

# return "TechlogTest.__repr__"

pass

if __name__ == '__main__':

testobj = TechlogTest()

print('%%r: %r; %%s: %s' % (testobj, testobj))

logging.info(testobj)

print(testobj)

print([testobj])

打印出了：%r: <__main__.techlogtest>; %s: <__main__.techlogtest>

[<__main__.techlogtest>]

我们看到，默认的实现方式通常不是我们想要的，他仅仅展示了对象在内存中的逻辑地址

只实现 __str__

import logging

logging.basicConfig(level=logging.INFO,

format='%(asctime)s - [line:%(lineno)d] - %(levelname)s: %(message)s')

class TechlogTest:

def __str__(self):

return "TechlogTest.__str__"

# def __repr__(self):

# return "TechlogTest.__repr__"

pass

if __name__ == '__main__':

testobj = TechlogTest()

print('%%r: %r; %%s: %s' % (testobj, testobj))

logging.info(testobj)

print(testobj)

print([testobj])

输出了：%r: <__main__.techlogtest>; %s: TechlogTest.__str__

2019-04-07 21:01:30,321 - [line:20] - INFO: TechlogTest.__str__

TechlogTest.__str__

[<__main__.techlogtest>]

我们看到，原本需要调用 __repr__ 变成了系统的默认实现

只实现 __repr__

import logging

logging.basicConfig(level=logging.INFO,

format='%(asctime)s - [line:%(lineno)d] - %(levelname)s: %(message)s')

class TechlogTest:

# def __str__(self):

# return "TechlogTest.__str__"

def __repr__(self):

return "TechlogTest.__repr__"

pass

if __name__ == '__main__':

testobj = TechlogTest()

print('%%r: %r; %%s: %s' % (testobj, testobj))

logging.info(testobj)

print(testobj)

print([testobj])

打印出了：%r: TechlogTest.__repr__; %s: TechlogTest.__repr__

2019-04-07 21:02:37,489 - [line:20] - INFO: TechlogTest.__repr__

TechlogTest.__repr__

[TechlogTest.__repr__]

所有需要调用 __str__ 的地方都改为调用了我们实现的 __repr__