11、python中的try/except/else/finally语句

用实例来解释下Python中的try/except/else/finally语句的执行顺序

1、如果try中的语句块执行成功，则会先执行try，再执行else，再执行finally

a='abc'
try:
print(a[0])
except IndexError as e:
print('AAA')
except IOError as e:
print('BBB')
else:
print('CCC')
finally:
print('DDD')

运行结果为：

C:\Python36\python.exe E:/python/test1/day5/try.py

a

CCC

DDD

2、如果try语句块未执行成功，出现异常，则从except中找对应的异常，能找到就打印，然后去执行finally

a='abc'
try:
print(a[9])
except IOError as e:
print('AAA')
except IndexError as e:
print('BBB')
else:
print('CCC')
finally:
print('DDD')

上面a[9] 会导致IndexError，即try语句块报IndexError异常，那么去第一个except找对应的错误，第一个是IOError，不匹配，继续从下面的except找，第二个是IndexError，匹配，执行该语句块，打印‘BBB’，然后打印finally语句。

执行结果：
C:\Python36\python.exe E:/python/test1/day5/try.py

BBB

DDD

3、如果try语句块未执行成功，出现异常，则从except中找对应的异常，当在所有的except中都找不到匹配的异常，则会将异常抛出，然后去执行finally。（并不是匹配不到执行else）

a='abc'
try:
print(a[9])
except IOError as e:
print('AAA')
except ImportError as e:
print('BBB')
else:
print('CCC')
finally:
print('DDD')

执行结果：

C:\Python36\python.exe E:/python/test1/day5/try.py

Traceback (most recent call last):

DDD

  File "E:/python/test1/day5/try.py", line 4, in <module>

    print(a[9])

IndexError: string index out of range

Process finished with exit code 1

4、如果我们想匹配不到异常则统一执行某个动作怎么办？使用except Exception as e语句

a='abc'
try:
print(a[9])
except IOError as e:
print('AAA')
except ImportError as e:
print('BBB')
except Exception as e:
print('EEE')
else:
prin
4000
t('CCC')
finally:
print('DDD')

执行结果：
C:\Python36\python.exe E:/python/test1/day5/try.py

EEE

DDD

Process finished with exit code 0