異常分為兩類，可預知和不可預知。

　　錯誤發生的條件如果是可以預知的，此時應該用if判斷去預防異常

AGE=10
age=input('>>: ').strip()

if age.isdigit():
    age=int(age)
    if age > AGE:
        print('太大了')

　　錯誤發生的條件如果是不可預知的，此時應該用異常處理機制，try...except

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

    print(next(f),end='')
    
 
print(next(f),end='')
    print(next(f),end='')
    print(next(f),end='')

    print(next(f),end='')
    print(next(f),end='')
    print(next(f),end='')
    f.close()
except StopIteration:
    print('出錯啦')

print('====>1')

#多分支：被監測的程式碼塊丟擲的異常有多種可能性，並且我們需要針對每一種異常型別都定製專門的處理邏輯
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')

#萬能異常：Exception,被監測的程式碼塊丟擲的異常有多種可能性，
 

# 並且我們針對所有的異常型別都只用一種處理邏輯就可以了，那就使用Exception
try:
    print('===>1')
    # name
    print('===>2')
    l=[1,2,3]
    l[100]
    print('===>3')
    d={}
    d['name']
    print('===>4')

except Exception as e:
    print('異常發生啦：',e)

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

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('統一的處理方法')


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

#其他結構
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('統一的處理方法')

else:
    print('在被檢測的程式碼塊沒有發生異常時執行')

finally:
    print('不管被檢測的程式碼塊有無發生異常都會執行')

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

# finally的應用
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()

　　自定義異常

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

    def __str__(self):
        return self.msg


try:
    raise XgError("自定義的異常！")

except Exception as e:
    print(e)