exceptions_handle.py

# 異常的處理
# try...except
# 通常的語句在try塊里  錯誤處理器放在except塊里


try:
    text = input('Enter something --> ')
except EOFError:
    print('Why did you do an EOF on me?')
except KeyboardInterrupt:
    print('You cancelled the operation.')
else:
    print('You entered {}'.format(text))
    
# 如果 except 后面不指定錯誤名稱 那么就是處理所有錯誤
# else 將在沒有發(fā)生異常的時候執(zhí)行

exceptions_raise.py

# 引發(fā)raise異常
# 要提供錯誤名或異常名以及要拋出Thrown的對象

class ShortInputException(Exception):
    '''一個由用戶定義的異常類'''
    def __init__(self,length,atleast):
        Exception.__init__(self)
        self.length = length
        self.atleast = atleast

try:
    text = input('Enter something --> ')
    if len(text) < 3:
        raise ShortInputException(len(text),3)
except EOFError:
    print('Why did you do an EOF on me?')
except ShortInputException as ex:
    print('ShortInputException: The input was ' + '{0} long, excepted at least {1}'.format(ex.length,ex.atleast))
else:
    print('No exception was raised.')

exceptions_finally.py

# try ... finally
# 主要是用在文件里面

import sys
import time

f = None
try:
    f = open('poem.txt')
    
    while True:
        line = f.readline()
        if len(line) == 0:
            break
        print(line,end='')
        # 以便print的內(nèi)容可以被立即打印到屏幕上
        sys.stdout.flush()
        print('Press ctrl+c now')
        
        # 每打印一行后插入兩秒休眠，讓程序運行得比較緩慢
        time.sleep(2)
except IOError:
    print('Could not find file poem.txt')
except KeyboardInterrupt:
    print('!! You cancelled the reading from the file.')
finally:
    if f:   # 這句話記得要
        f.close()
    print('(Clearning up:Closed the file)')

exceptions_using_with.py

# 在try塊中獲取資源（也就是open） 然后在finally塊中釋放資源（也就是close()）
# with語句可以很簡單做到這一模式

with open('opem.txt') as f:
    for line in f:
        print(line,end='')

# 文件的關閉交由with ... open來完成
# with 會獲取open返回的對象f
# 然后在代碼塊開始之前調(diào)用 f.__enter__函數(shù) 
# 在代碼塊結(jié)束之后調(diào)用 f.__exit__函數(shù)