python - 异常必须是旧式类或派生自 BaseException，而不是 NoneType

Question

在执行下面的代码时，如果由于某种原因无法获取 firefox 配置文件/webdriver，我会收到以下错误消息:

exceptions must be old-style classes or derived from BaseException, not NoneType

我想了解为什么在这种情况下会显示此错误:

self.error = 0  
self.profile, profileErrStatus = self.GetFireFoxProfile(path)
if self.profile:
  self.driver, driverErrStatus = self.GetFireFoxWebDriver(self.profile)
  if self.driver:
  else:
    print('Failed to get Firefox Webdriver:%s'%(str(sys.exc_info()[0])))
    raise
else:
  print('Failed to get Firefox Profile:%s'%(str(sys.exc_info()[0])))
  raise   

Answer 1

这是因为您在使用 raise 时没有提供异常类型或实例。

根据documentation :

The sole argument to raise indicates the exception to be raised. This must be either an exception instance or an exception class (a class that derives from Exception).

演示:

>>> raise
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: exceptions must be old-style classes or derived from BaseException, not NoneType

>>> raise ValueError('Failed to get Firefox Webdriver')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Failed to get Firefox Webdriver

请注意，可以在 except block 中使用不带参数的 raise 来重新引发异常。

---

仅供引用，在 python3 上，它会引发 RuntimeError 而不是:

>>> raise
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: No active exception to reraise