Python基础-异常处理

python的异常处理机制，由try,except,raise,else,finally关键字构成

异常基本用法
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"""
python 异常关键字 try except else finally raise
try:
    statement..
    (raise...)
except EX:
    statement
else:
    statement
finally:
    statement
except 块可以多个 捕获相应的异常后进入相应的except块 父类放在最后
else 在主代码没有异常的情况下继续需要执行的代码
finally 是否有异常最终都会执行
python 异常都继承BaseException
主要子类为Exception 自定义需要继承Exception

"""


def divide(n):
    try:
        a = 10
        b = 10 / n
        print("divide result:", b)
    except TypeError:
        print("type error...")
    except ArithmeticError:
        print("arithmetic error ...")
    else:
        print("this is else block")
    finally:
        print("this is finally block")
        print("-----------------------")


divide("haha")
divide(0)
divide(2)
"""
python 也可以同时捕获多个异常
"""


def divide_two(n):
    try:
        a = 10
        b = 10 / n
        print("divide result:", b)
    except (TypeError, ArithmeticError):
        print("some error...")


divide_two(0)
"""
访问异常信息 可以直接打印异常信息
"""


def divide_three(n):
    try:
        a = 10
        b = a / n
        print("divide result:", b)
    except Exception as e:
        print(e.args)
        print(e)
        print(str(e))


divide_three(0)
"""
finally 不执行的情况  在try或者except块中使用了
退出解释器的方法 finally块会不执行 应避免这种情况
"""
import os


def divide_three(n):
    try:
        a = 10
        b = a / n
        print("divide result:", b)
        os._exit(1)
    except Exception as e:
        print("this is error block")
        os._exit(1)
    finally:
        # finally 块无法执行
        print("this is finally")


#divide_three(0)
divide_three(2)
raise用法以及自定义异常
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"""
raise 引发异常 每次只能引发一个异常实例
raise 单独使用，后面也可以跟着异常类或者异常实例
"""


def raise_test(n):
    if n == 1:
        raise
    elif n == 2:
        raise TypeError
    elif n == 3:
        raise ValueError("this is value error")
    else:
        print("no error")


def main_test(m):
    try:
        raise_test(m)
    except Exception as e:
        print("Error:", str(e))


main_test(1)
"""
自定义异常 继承Exception或者Exception子类
"""


class MyError(Exception):
    pass


def myError_test(n):
    if n == 1:
        raise MyError("this is my error")


def my_error(m):
    try:
        myError_test(m)
    except Exception as e:
        print(e)
        raise  # 当前error继续向上抛出


my_error(1)