Use attrs when a class calls `super`

[felipedau]

I could not use attrs in the Introduction class because it inherits from Thread and I have not found a way to call super. Example:

>>> @attr.s
... class T(Thread, object):
...     def __attr_post_init__(self):
...             super(T, self).__init__()
... 
>>> t = T()
>>> t.start()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/threading.py", line 737, in start
    raise RuntimeError("thread.__init__() not called")
RuntimeError: thread.__init__() not called

@meejah, do you have an idea on how to do this?

[felipedau]

As I continued working on #21, I noticed there was no need to subclass Thread in Introduction and now there is no need to fix this. Anyways, here is some useful info:

• When I tried to reproduce the error, I made a mistake: wrote __attr_post_init__ instead of __attrs_post_init__
• That method would never be called, along with super().__init__() inside it
• Due to the mistake, I thought that Thread.__init__() not being called was the issue I had in the first place
• When fixing the typo, the real issue is actually TypeError: unhashable type
• Passing hash=True to @attr.s() makes it hashable