exceptions_handle.py
# 异常的处理
# try...except
# 通常的语句在try块里 错误处理器放在except块里
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 后面不指定错误名称 那么就是处理所有错误
# else 将在没有发生异常的时候执行
exceptions_raise.py
# 引发raise异常
# 要提供错误名或异常名以及要抛出Thrown的对象
class ShortInputException(Exception):
'''一个由用户定义的异常类'''
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的内容可以被立即打印到屏幕上
sys.stdout.flush()
print('Press ctrl+c now')
# 每打印一行后插入两秒休眠，让程序运行得比较缓慢
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: # 这句话记得要
f.close()
print('(Clearning up:Closed the file)')
exceptions_using_with.py
# 在try块中获取资源（也就是open） 然后在finally块中释放资源（也就是close()）
# with语句可以很简单做到这一模式
with open('opem.txt') as f:
for line in f:
print(line,end='')
# 文件的关闭交由with ... open来完成
# with 会获取open返回的对象f
# 然后在代码块开始之前调用 f.__enter__函数
# 在代码块结束之后调用 f.__exit__函数
