I was using the telnetlib on linux in python 2.7 and ran into error that executed line 320 of https://hg.python.org/cpython/file/2.7/Lib/telnetlib.py 

----------------------------------
319: except select.error as e:
320:    if e.errno == errno.EINTR:
------------------------------------

Inspecting select.error showed that it has no errno attribute.

I opened up a python2.7 idle session on my computer and entered the following. 


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>>> import select
>>> try:
...     raise select.error
... except Exception as e:
...     pass
... 
>>> e
error()
>>> dir(e)
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__getitem__', '__getslice__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setstate__', '__sizeof__', '__str__', '__subclasshook__', '__unicode__', '__weakref__', 'args', 'message']
>>> e.errno
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'error' object has no attribute 'errno'
>>> 
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In py2, select.error is a stand alone exception while in py3 it's an alias of OSError. This difference seems not noticed when introduced in 872afada51b0.

Thanks for the report. This is a duplicate of issue 18035.