python assert的用处示例详解

assert expression [, arguments]
assert 表达式 [, 参数]

a = 1
assert a < 0, '出错了,a大于0 啊'
print('这里不会输出')

Traceback (most recent call last):
 File "main.py", line 3, in <module>
 assert a < 0, '出错了,a大于0 啊'
AssertionError: 出错了,a大于0 啊

a = 1
b = -1
assert a > 0, b < 0
print('正常输出,表达式返回真了') # 输出：正常输出,表达式返回真了

import traceback

try:
 assert a < 0
except AssertionError as aeeor: # 明确抛出此异常
 # 抛出 AssertionError 不含任何信息，所以无法通过 aeeor.__str__()获取异常描述
 print('AssertionError', aeeor, aeeor.__str__())

 # 通过 traceback 打印详细异常信息
 print('traceback 打印异常')
 traceback.print_exc()
except: # 不会命中其他异常
 print('assert except')

try:
 raise AssertionError('测试 raise AssertionError')
except AssertionError as aeeor:
 print('raise AssertionError 异常', aeeor.__str__())

AssertionError
 traceback 打印异常
 Traceback (most recent call last):
 File "main.py", line 7, in <module>
 aAssertionError
 raise AssertionError 异常 测试 raise AssertionErrorssert a < 0

# 除法运算
def foo(value, divide):
 assert divide != 0
 return value / divide
print('4除以2 =', foo(4, 2)) # 执行成功
print('4除以0 =', foo(4, 0)) # 抛出异常

 4除以2 = 2.0
 Traceback (most recent call last):
 File "main.py", line 8, in <module>
 print('4除以0 =', foo(4, 0)) # 抛出异常
 File "main.py", line 3, in foo
 assert divide != 0
 AssertionError