Log Message:
py-attrs: updated to 17.3.0

17.3.0:

Backward-incompatible Changes
- Attributes are not defined on the class body anymore.
  This means that if you define a class C with an attribute x, the class will \ 
*not* have an attribute x for introspe
ction anymore.
  Instead of C.x, use attr.fields(C).x or look at C.__attrs_attrs__.
  The old behavior has been deprecated since version 16.1.

Changes
- super() and __class__ now work on Python 3 when slots=True.
- Added type argument to attr.ib() and corresponding type attribute to \ 
attr.Attribute.

  This change paves the way for automatic type checking and serialization \ 
(though as of this release attrs does not make use of it).
  In Python 3.6 or higher, the value of attr.Attribute.type can alternately be \ 
set using variable type annotations
- The combination of str=True and slots=True now works on Python 2.
- attr.Factory is hashable again.
- Subclasses now can overwrite attribute definitions of their superclass.

  That means that you can -- for example -- change the default value for an \ 
attribute by redefining it.
- Added new option auto_attribs to @attr.s that allows to collect annotated \ 
fields without setting them to attr.ib().

  Setting a field to an attr.ib() is still possible to supply options like \ 
validators.
  Setting it to any other value is treated like it was passed as \ 
attr.ib(default=value) -- passing an instance of attr.Factory also works as \ 
expected.