try-except

try:
	正常程序
except:
	抛出异常

try:
 # 正常程序
 ipt = input("请输入：")
 num = int(ipt) #ValueError
 print(num)
except Exception as e:
    # 一旦有异常，执行except内部块
    print(e)
    num = 1
    print(num)
    
 请输入：1.5
invalid literal for int() with base 10: '1.5'
 1

try:
    # li = [2 , 3]
    # li[2] # IndexError

    a = 2
    b = 0
    c = a/b  # ZeroDivisionError
except IndexError as e:
    print(e)
except ZeroDivisionError as e:
    print(e)
except Exception as e:
    print(e)
else:
    print("如果没错~执行else代码")
finally:
    print("不管有无异常都执行")

'''
主动抛出异常
'''
def test(time):
    if time<5:
        raise Exception("错误")
try:
    test(4)
except Exception as e:
    print(e)
else:
    print("成功")

def db():
    raise Exception("数据库的错误")
def demo():
    try:
        db()
    except Exception as e:
        print(e,'111')

    try:
        li = [2,3]
        li[3]
    except Exception as e:
        print(e,'111')

demo()

class OldAmyError(Exception):
    def __init__(self,msg):
        self.msg_err = msg
    def __str__(self):
        return self.msg_err

# obj = OldAmyError("报错")
# print(obj)
try:
    raise OldAmyError("电脑错了。。") # 实例化类
except OldAmyError as e:
    print(e)

'''
断言
用于强制用户服从，可捕获也可不
'''

print('---1---') #AssertionError
assert 1==2
print('22222222')