assert condition    相当于     if not condition:        crash program    断言设置的目的就是因为与其让程序晚点崩溃，不如直接设置错误情况，让它直接崩溃    >>> age = -1    >>> assert 0 < age < 100    AssertionError

    try:        x = input()        y = input()        print(x/y)    except ZeroDivisionError:        print("Division by Zero")    类似这样try/except形式就是来捕捉可能发生的异常错误，一旦出现ZeroDivisionError错误信息，则运行except ZeroDivisionError之后的代码    通过多个except来捕捉不同错误信息        def calc(expr):            try:                return eval(expr)            except ZeroDivisionError:                print("Divison by zero")            except TypeError:                print(‘This is not a number?‘)    一个块捕捉多个错误信息        def calc(expr):            try:                return eval(expr)            except (ZeroDivisionError, TypeError):                print("Input has some bugs")    打印错误信息        def calc(expr):            try:                return eval(expr)            except (ZeroDivisionError, TypeError) as error:                print(error)    对于其他错误信息处理        def calc(expr):            try:                return eval(expr)            except ZeroDivisionError:                print("Divison by zero")            except:                print(‘haha, something unknown happened!‘)    else语句用于不出现错误信息        def calc(expr):            try:                return eval(expr)            except ZeroDivisionError:                print("Divison by zero")            else:                print("Oh, it goes well!")    此外还有finally语句，无论是否错误均会执行    实际应用：(输入表达式直到可以计算)    while True:        try:            print(eval(input()))        except:            print(‘Please reinput until you input the correct expression!‘)        else:            break;        finally:            print(‘I love the world whatever!‘) #即使else中break也会执行finally