Log Message:
Changes 17.1.0:
Backward-incompatible changes:
* attrs will set the __hash__() method to None by default now. The way hashes \ 
were handled before was in conflict with Python’s specification. This may \ 
break some software although this breakage is most likely just surfacing of \ 
latent bugs. You can always make attrs create the __hash__() method using \ 
@attr.s(hash=True).
* Correspondingly, attr.ib‘s hash argument is None by default too and \ 
mirrors the cmp argument as it should.

Deprecations:
* attr.assoc() is now deprecated in favor of attr.evolve() and will stop working \ 
in 2018.

Changes:
Fix default hashing behavior. Now hash mirrors the value of cmp and classes are \ 
unhashable by default.
Added attr.evolve() that, given an instance of an attrs class and field changes \ 
as keyword arguments, will instantiate a copy of the given instance with the \ 
changes applied. evolve() replaces assoc(), which is now deprecated. evolve() is \ 
significantly faster than assoc(), and requires the class have an initializer \ 
that can take the field values as keyword arguments (like attrs itself can \ 
generate).
FrozenInstanceError is now raised when trying to delete an attribute from a \ 
frozen class.
Frozen-ness of classes is now inherited.
__attrs_post_init__() is now run if validation is disabled.
Added attr.validators.in_(options) that, given the allowed options, checks \ 
whether the attribute value is in it. This can be used to check constants, \ 
enums, mappings, etc.
Added attr.validators.and_() that composes multiple validators into one.
For convenience, the validator argument of @attr.s now can take a list of \ 
validators that are wrapped using and_().
Accordingly, attr.validators.optional() now can take a list of validators too.
Validators can now be defined conveniently inline by using the attribute as a \ 
decorator. Check out the examples to see it in action!
attr.Factory() now has a takes_self argument that makes the initializer to pass \ 
the partially initialized instance into the factory. In other words you can \ 
define attribute defaults based on other attributes.
Default factories can now also be defined inline using decorators. They are \ 
always passed the partially initialized instance.
Conversion can now be made optional using attr.converters.optional().
attr.make_class() now accepts the keyword argument bases which allows for \ 
subclassing.
Metaclasses are now preserved with slots=True.