断言assert

1 info = {} 2 info['name'] = 'alex' 3 # info['age'] = 18 4  5 if 'name' not in info: 6     raise KeyError('必须有name这个key') 7 if 'age' not in info: 8     raise KeyError('必须有age这个key') 9 10 结果为：11 12 Traceback (most recent call last):13   File "C:/Users/xu516/PycharmProjects/Python全栈开发/第三模块/面向对象编程/33 try...except详细用法.py", line 68, in 
     
      14     raise KeyError('必须有age这个key')15 KeyError: '必须有age这个key'
     

断言是断定会有什么，没有的话就会报错，可以用assert方法来实现，如下：

1 info = {} 2 info['name'] = 'alex' 3 # info['age'] = 18 4  5 # if 'name' not in info: 6 #     raise KeyError('必须有name这个key') 7 # if 'age' not in info: 8 #     raise KeyError('必须有age这个key') 9 10 assert ('name' in info) and ('age' in info)11 12 结果为：13 14 Traceback (most recent call last):15   File "C:/Users/xu516/PycharmProjects/Python全栈开发/第三模块/面向对象编程/33 try...except详细用法.py", line 70, in 
     
      16     assert ('name' in info) and ('age' in info)17 AssertionError
     

断言报错，

1 info = {} 2 info['name'] = 'alex' 3 info['age'] = 18 4  5 # if 'name' not in info: 6 #     raise KeyError('必须有name这个key') 7 # if 'age' not in info: 8 #     raise KeyError('必须有age这个key') 9 10 assert ('name' in info) and ('age' in info)11 12 if info['name'] == 'alex' and info['age'] > 10:13     print('welcome')14 15 结果为：16 17 welcome

if 语句的执行依赖于前面代码执行结果