异常Exception

2019年11月27日

# coding=utf-8

import datetime as dt

def read_date(in_date):
    try:
        tmpDate = dt.datetime.strptime(str_date, '%Y-%m-%d')
        return tmpDate
    except Exception as e:
        print('处理异常')
        print(e)

# 非法时间 直接调用会报异常
str_date = '2011-13-18'
print('日期 = {0}'.format(read_date(str_date)))

/usr/local/bin/python3.8 /Users/mac/Documents/wangyu/gitRepository/HelloProj/com/pkg1/Hello.py

处理ValueError异常

time data '2011-13-18' does not match format '%Y-%m-%d'

日期 = None

Process finished with exit code 0

二.多重异常捕获
1.用法1

# coding=utf-8

import datetime as dt

def read_date_from_file(filename):
    try:
        file = open(filename)
        in_date = file.read()
        in_date = in_date.strip()
        date = dt.datetime.strptime(in_date, '%Y-%m-%d')
        return date
    except ValueError as e:
        print('处理ValueError异常')
        print(e)
    except FileNotFoundError as e:
        print('处理FileNotFoundError异常')
        print(e)
    except OSError as e:
        print('处理OSError异常')
        print(e)

date = read_date_from_file('readme.txt')
print('日期 = {0}'.format(date))

1.1 添加finally 用法 推荐用下面的1.2 with as

# coding=utf-8

import datetime as dt

def read_date_from_file(filename):
    try:
        file = open(filename)
    except OSError as e:
        print('打开文件失败')
    else:
        print('打开文件成功')
        try:
            in_date = file.read()
            in_date = in_date.strip()
            date = dt.datetime.strptime(in_date, '%Y-%m-%d')
            return date
        except ValueError as e:
            print('处理ValueError异常')
        except OSError as e:
            print('处理OSError异常')
        finally:
            file.close()

date = read_date_from_file('readme.txt')
print('日期 = {0}'.format(date))

1.2 with as用法 解决上面代码层级混乱问题 【with as 提供一个代码块，在as后面声明的资源变量，会等with as代码块执行完后，自动释放】

import datetime as dt

def read_date_from_file(filename):
    try:
        with open(filename) as file:
            in_date = file.read()

        in_date = in_date.strip()
        date = dt.datetime.strptime(in_date, '%Y-%m-%d')
        return date
    except ValueError as e:
        print('处理ValueError异常')
    except OSError as e:
        print('处理OSError异常')

date = read_date_from_file('readme.txt')
print('日期 = {0}'.format(date))

2.用法2 注意（OSError可以捕获所有他的子类异常）

import datetime as dt

def read_date_from_file(filename):
    try:
        file = open(filename)
        in_date = file.read()
        in_date = in_date.strip()
        date = dt.datetime.strptime(in_date, '%Y-%m-%d')
        return date
    except (ValueError, OSError) as e:
        print('调用方法method1处理...')
        print(e)

date = read_date_from_file('readme.txt')
print('日期 = {0}'.format(date))

三.打印详细的异常堆栈信息

import datetime as dt
import traceback as tb

def read_date_from_file(filename):
    try:
        file = open(filename)
        in_date = file.read()
        in_date = in_date.strip()
        date = dt.datetime.strptime(in_date, '%Y-%m-%d')
        return date
    except (ValueError, OSError) as e:
        print('调用方法method1处理...')
        tb.print_exc()

date = read_date_from_file('readme.txt')
print('日期 = {0}'.format(date))

注意不会报错，只会输出日志信息

image.png

四.自定义异常

import datetime as dt

class MyException(Exception):
    def __init__(self, message):
        super().__init__(message)

def read_date_from_file(filename):
    try:
        file = open(filename)
        in_date = file.read()
        in_date = in_date.strip()
        date = dt.datetime.strptime(in_date, '%Y-%m-%d')
        return date
    except ValueError as e:
        raise MyException('不是有效的日期')
    except FileNotFoundError as e:
        raise MyException('文件找不到')
    except OSError as e:
        raise MyException('文件无法打开或无法读取')

date = read_date_from_file('readme.txt')
print('日期 = {0}'.format(date))

image.png

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