>>> from copy import deepcopy
>>> import attr
>>> @attr.s
... class Foo(Exception):
...     bar = attr.ib()
...
>>> deepcopy(Foo(1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 190, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 329, in _reconstruct
    y = callable(*args)
TypeError: __init__() takes exactly 2 arguments (1 given)

>>> from copy import deepcopy
>>> import attr
>>> @attr.s
... class Foo(Exception):
...     bar = attr.ib()
...
>>> deepcopy(Foo(1))
Foo(bar=1)