错误处理

try、except、finally

先执行try中的语句，如果发生了错误则被except捕获，否则无错误则执行else语句，最终执行finally语句

try:
    print('try...')
    r = 10 / int('2')
    print('result:', r)
except ValueError as e:
    print('ValueError:', e)
except ZeroDivisionError as e:
    print('ZeroDivisionError:', e)
else:
    print('no error!')
finally:
    print('finally...')
print('END')

try...
result: 5.0
no error!
finally...
END

抛出异常

异常本身也是类

class FooError(ValueError):#定义异常
    pass

def foo(s):
    n = int(s)
    if n==0:
        raise FooError('无效的值: %s' % s)#抛出异常
    return 10 / n

foo('0')

---------------------------------------------------------------------------

FooError                                  Traceback (most recent call last)

<ipython-input-10-0c3ece3b8a4a> in <module>
      8     return 10 / n
      9 
---> 10 foo('0')


<ipython-input-10-0c3ece3b8a4a> in foo(s)
      5     n = int(s)
      6     if n==0:
----> 7         raise FooError('无效的值: %s' % s)#抛出异常
      8     return 10 / n
      9 


FooError: 无效的值: 0

直接使用rasie,不带任何内容是直接抛出错误

def foo(s):
    n = int(s)
    if n==0:
        raise ValueError('invalid value: %s' % s)
    return 10 / n

def bar():
    try:
        foo('0')
    except ValueError as e:
        print('ValueError!')
        raise #继续抛出当前错误

bar()

ValueError!



---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

<ipython-input-11-2304461f3f2b> in <module>
     12         raise #继续抛出当前错误
     13 
---> 14 bar()


<ipython-input-11-2304461f3f2b> in bar()
      7 def bar():
      8     try:
----> 9         foo('0')
     10     except ValueError as e:
     11         print('ValueError!')


<ipython-input-11-2304461f3f2b> in foo(s)
      2     n = int(s)
      3     if n==0:
----> 4         raise ValueError('invalid value: %s' % s)
      5     return 10 / n
      6 


ValueError: invalid value: 0

assert断言

assert 条件 , 抛出AssertionError异常携带的信息

eg:assert n!=0,'n is zero!'

在运行python文件的时候可以关闭断言开关python -O xxx.py,此处为大写字母O，不是数字0

def foo(s):
    n = int(s)
    assert n != 0, 'n is zero!'
    return 10 / n

foo('0')

---------------------------------------------------------------------------

AssertionError                            Traceback (most recent call last)

<ipython-input-24-1d060d98ffe3> in <module>
      4     return 10 / n
      5 
----> 6 foo('0')


<ipython-input-24-1d060d98ffe3> in foo(s)
      1 def foo(s):
      2     n = int(s)
----> 3     assert n != 0, 'n is zero!'
      4     return 10 / n
      5 


AssertionError: n is zero!

logging模块

在运行文件的时候才会有效果 交互模式下不显示

import logging# 导入logging的包
logging.basicConfig(level=logging.INFO)#日志输出级别设置为info

logging.info('123456')#输出

INFO:root:n = 0
Traceback (most recent call last):
  File "test.py", line 7, in <module>
    print(10 / n)
ZeroDivisionError: division by zero

单元测试

先写一个用于被测试的类

class Dict(dict):
    def __init__(self, **kw):
        super().__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

# 它的使用方法如下
d = Dict(a=1, b=2)
print(d['a'])
print(d.b)

1
2

编写单元测试类

import unittest #导入单元测试模块

class TestDict(unittest.TestCase):#编写单元测试类，继承unittest.TestCase

    #编写单元测试方法  必须以test开头
    def test_init(self):
        d = Dict(a=1, b='test')
        self.assertEqual(d.a, 1)#unittest.TestCase自带的断言方法
        self.assertEqual(d.b, 'test')
        self.assertTrue(isinstance(d, dict))

    def test_key(self):
        d = Dict()
        d['key'] = 'value'
        self.assertEqual(d.key, 'value')

    def test_attr(self):
        d = Dict()
        d.key = 'value'
        self.assertTrue('key' in d)
        self.assertEqual(d['key'], 'value')

    def test_keyerror(self):
        d = Dict()
        with self.assertRaises(KeyError):#unittest.TestCase期待抛出错误KeyError
            value = d['empty']

    def test_attrerror(self):
        d = Dict()
        with self.assertRaises(AttributeError):#unittest.TestCase期待抛出错误AttributeError
            value = d.empty

运行单元测试

方法1

直接在代码中加入

if __name__ == '__main__':
    unittest.main()

然后直接运行该文件 python xxx.py

方法2

在命令行输入python -m unittest xxx,其中xxx为不带后缀名py的文件名

单元测试中的两个特殊方法setUp与tearDown

分别在每个测试方法前后执行

比如测试方法需要连接数据库，可以在setUp方法中打开数据库连接，在tearDown方法中关闭数据库的连接

class TestDict1(unittest.TestCase):

    def setUp(self):
        print('setUp...')

    def tearDown(self):
        print('tearDown...')

本文地址：https://blog.csdn.net/qq754772661/article/details/107080396