捕获多个异常
将异常类型放入元组之中即可：
try:
...
except (URLError, ValueError):
log('Reason:', e)捕获所有异常
try:
...
except Exception as e:
...
log('Reason:', e)捕获除了 SystemExit 、 KeyboardInterrupt 和 GeneratorExit 之外的所有异常，如果需捕获这三个异常，可修改为：
try:
...
except BaseException as e:
...
log('Reason:', e)