Py003-01-15异常操作方式

异常的处理

多分支

被监测的代码块抛出的异常有多种可能性，并且我们需要针对每一种异常类型都定制专门的处理逻辑

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try:
    print('===>1')
    # name
    print('===>2')
    l=[1,2,3]
    # l[100]
    print('===>3')
    d={}
    d['name']
    print('===>4')

except NameError as e:
    print('--->',e)

except IndexError as e:
    print('--->',e)

except KeyError as e:
    print('--->',e)

print('====>afer code')

万能异常：Exception

  • 被监测的代码块抛出的异常有多种可能性，
  • 并且我们针对所有的异常类型都只用一种处理逻辑就可以了，那就使用Exception
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try:
    print('===>1')
    # name
    print('===>2')
    l=[1,2,3]
    l[100]
    print('===>3')
    d={}
    d['name']
    print('===>4')

except Exception as e:
    print('异常发生啦：',e)

print('====>afer code')
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try:
    print('===>1')
    # name
    print('===>2')
    l=[1,2,3]
    # l[100]
    print('===>3')
    d={}
    d['name']
    print('===>4')

except NameError as e:
    print('--->',e)

except IndexError as e:
    print('--->',e)

except KeyError as e:
    print('--->',e)

except Exception as e:
    print('统一的处理方法')


print('====>afer code')

其他结构

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try:
    print('===>1')
    # name
    print('===>2')
    l=[1,2,3]
    # l[100]
    print('===>3')
    d={}
    d['name']
    print('===>4')

except NameError as e:
    print('--->',e)

except IndexError as e:
    print('--->',e)

except KeyError as e:
    print('--->',e)

except Exception as e:
    print('统一的处理方法')

else:
    print('在被检测的代码块没有发生异常时执行')

finally:
    print('不管被检测的代码块有无发生异常都会执行')



print('====>afer code')

# 回收资源

try:
    f=open('a.txt','r',encoding='utf-8')
    print(next(f))
    print(next(f))
    print(next(f))
    print(next(f))

    print(next(f))
    print(next(f))
finally:
    f.close()

主动触发异常：raise 异常类型(值)

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class People:
    def __init__(self,name,age):
        if not isinstance(name,str):
            raise TypeError('名字必须传入str类型')
        if not isinstance(age,int):
            raise TypeError('年龄必须传入int类型')
        self.name=name
        self.age=age

p=People('egon',18)

自定义异常类型

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class MyException(BaseException):
    def __init__(self,msg):
        super(MyException,self).__init__()
        self.msg=msg

    def __str__(self):
        return '<%s>' %self.msg

raise MyException('我自己的异常类型') #print(obj)

断言assert

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info={}
info['name']='hjx'
# info['age']=18


# if 'name' not in info:
#     raise KeyError('必须有name这个key')
#
# if 'age' not in info:
#     raise KeyError('必须有age这个key')

assert ('name' in info) and ('age' in info)



if info['name'] == 'hjx' and info['age'] > 10:
    print('welcome')

万能异常(铁定不出错)

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try:
    pass


except Exception:
    pass