可能触发异常产生的代码会放到try语句块里,而处理异常的代码会在except语句块里实现。例如:
try:
file = open('test.txt', 'rb')
except IOError as e:
print('An IOError occurred. {}'.format(e.args[-1]))
我们可以使用三种方法来处理多个异常。
第一种方法需要把所有可能发生的异常放到一个元组里。像这样:
try:
file = open('test.txt', 'rb')
except (IOError, EOFError) as e:
print("An error occurred. {}".format(e.args[-1]))
另外一种方式是对每个单独的异常在单独的except语句块中处理。我们想要多少个except语句块都可以:
try:
file = open('test.txt', 'rb')
except EOFError as e:
print("An EOF error occurred.")
raise e
except IOError as e:
print("An error occurred.")
raise e
最后一种方式会捕获所有异常:
try:
file = open('test.txt', 'rb')
except Exception as e:
# Some logging if you want
raise e
注意,捕获所有异常可能会造成意外的结果,比如,通常我们使用CTRL+C来终止程序,但如果程序中捕获了所有异常,CTRL+C就无法终止程序了。
包裹到finally从句中的代码不管异常是否触发都将会被执行。这可以被用来在脚本执行之后做清理工作:
try:
file = open('test.txt', 'rb')
except IOError as e:
print('An IOError occurred. {}'.format(e.args[-1]))
finally:
print("This would be printed whether or not an exception occurred!")
# Output: An IOError occurred. No such file or directory
# This would be printed whether or not an exception occurred!
如果想在没有触发异常的时候执行一些代码,可以使用else从句。
有人也许问了:如果你只是想让一些代码在没有触发异常的情况下执行,为啥你不直接把代码放在try里面呢?回答是,那样的话这段代码中的任意异常都还是会被try捕获,而你并不一定想要那样。
try:
print('I am sure no exception is going to occur!')
except Exception:
print('exception')
else:
# any code that should only run if no exception occurs in the try,
# but for which exceptions should NOT be caught
print('This would only run if no exception occurs. And an error here '
'would NOT be caught.')
finally:
print('This would be printed in every case.')
# Output: I am sure no exception is going to occur!
# This would only run if no exception occurs. And an error here would NOT be caught
# This would be printed in every case.
else从句只会在没有异常的情况下执行,而且它会在finally语句之前执行。
本文来自投稿,不代表重蔚自留地立场,如若转载,请注明出处https://www.cwhello.com/44684.html
如有侵犯您的合法权益请发邮件951076433@qq.com联系删除