Python异常处理

day25

参考：http://www.cnblogs.com/wupeiqi/p/5017742.html

while True:
    try:
        #
        inp = input('请输入序号：')
        i = int(inp)

    except Exception as e:
        print(e)
        i = 1

    print(i)

执行结果：

请输入序号：8
8
请输入序号：9
9
请输入序号：yu
invalid literal for int() with base 10: 'yu'
1
请输入序号：

IndexError,ValueError等是Exception的子类

#IndexError,ValueError等是Exception的子类
try:
    li = [11, 22]
    li[999]

except IndexError as e:
    print(e)

执行结果：

list index out of range

Process finished with exit code 0

else，finall

try:

    int('9a')

except IndexError as e:
    print('IndexError',e)
except ValueError as e:
    print('ValueError',e)
except Exception as e:
    print('Exception',e)
else:
    print('else')#正确，则执行
finally:
    print('.....')#无论如何都执行

若正确则执行else中内容，而finally中内容必须执行。

执行结果：

ValueError invalid literal for int() with base 10: '9a'
.....

Process finished with exit code 0

主动触发异常、自定义异常、断言

#主动触发异常
def db():
    return False

def index():
    try:
        result = db()
        if not result:
            raise Exception('数据库处理错误')#处理信息
    except Exception as e:
        str_error = str(e)
        print(str_error)#出错则输出：数据库处理错误

index()

# try:
#     raise Exception('不过了......')#主动触发异常
# except Exception as e:
#     print(e)


#自定义异常
class OldBoyError(Exception):#继承Exception

    def __init__(self, msg):
        self.message = msg

    def __str__(self):
        return self.message

# obj = OldBoyError('xxx')
# print(obj)
try:
    raise OldBoyError('我错了...')
except OldBoyError as e:
    print(e)# e对象的__str__()方法，获取返回


#断言,用于强制用户服从，可捕获，但一般不捕获。
print(123)
assert 1 == 2 #后面为条件
print(456)

执行结果：

数据库处理错误
我错了...
123
Traceback (most recent call last):
  File "/home/nizhipeng/PycharmProjects/learnPython/day25/异常处理.py", line 82, in <module>
    assert 1 == 2 #后面为条件
AssertionError

Process finished with exit code 1