没有异常处于活动状态时，Python 3跟踪失败

Question

我注意到在Python2中，当我尝试转储异常堆栈跟踪，但没有活动异常时，它会打印None：

Python 2.7.2+ (default, Oct  4 2011, 20:06:09) 
>>> import traceback
>>> traceback.print_exc()
None

但Python3因内部问题而失败：

Python 3.2.2 (default, Sep  5 2011, 21:17:14) 
>>> import traceback
>>> traceback.print_exc()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.2/traceback.py", line 259, in print_exc
    print_exception(etype, value, tb, limit, file, chain)
  File "/usr/lib/python3.2/traceback.py", line 155, in print_exception
    for value, tb in values:
  File "/usr/lib/python3.2/traceback.py", line 122, in _iter_chain
    cause = exc.__cause__
AttributeError: 'NoneType' object has no attribute '__cause__'

这是Python中的错误，还是我应该在调用print_exc()

之前测试某些条件

Answer 1

That is a bug。可能会决定应该引发错误，但这肯定是错误的错误。