Python基础教程之错误和异常的处理方法

# 异常的捕获
a=int(input('输入除数:'))
b=int(input('输入被除数:'))
try:
    res=a/b
except ZeroDivisionError:
    print('除数不可以为0')
    # 相同处理方式的异常可以这么写
except (BaseException,TypeError):
    print('有错误')
else:
    print('您的结果为',res)
finally:
    print('感谢使用!')

'''
3 录入一个学生的成绩，把该学生的成绩转换为A优秀、B良好、C合格、D不及格的形式，
最后将该学生的成绩打印出来。要求使用assert断言处理分数不合理(小于0或者大于100)的情况
请编写程序。
'''

n=int(input())
assert n in range(101),"您输入的成绩不合理！"
if n>=85:
	print("优秀！")
elif n>=70:
	print("良好！")
elif n>=60:
	print("合格！")
else:
	print("不及格！")

'''
自己定义一个异常类，继承Exception类, 捕获下面的过程：判断input()输入的字符串长度是否小于5， 
如果小于5，比如输入长度为3则输出:"The input is of length 3, expecting at least 5“，
大于5则输出"success”。 
'''
class StrLenError(Exception):
	def __init__(self,s):
		Exception.__init__(self,s)
		self.s =s
	def __str__(self):
			return f"The input is of length {len(self.s)}, expecting at least 5"
n=input()
if len(n)<=5:
	raise StrLenError(n)
else:
	print("success")

>>> class NewError(Exception):
        def __init__(self, value):
            self.value = value
        def __str__(self):
            return repr(self.value)
   
>>> try:
        raise NewError(2*2)
    except NewError as e:
        print('New exception occurred, value:', e.value)
   
My exception occurred, value: 4
>>> raise NewError('oops!')
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
__main__.NewError: 'oops!'

class Error(Exception):
    """Base class for exceptions in this module."""
    pass

class InputError(Error):
    """Exception raised for errors in the input.

    Attributes:
        expression -- input expression in which the error occurred
        message -- explanation of the error
    """

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

class TransitionError(Error):
    """Raised when an operation attempts a state transition that's not
    allowed.

    Attributes:
        previous -- state at beginning of transition
        next -- attempted new state
        message -- explanation of why the specific transition is not allowed
    """

    def __init__(self, previous, next, message):
        self.previous = previous
        self.next = next
        self.message = message