Support for multi-level inheritance

[cournape]

I was quite excited to see characteristic improved to use descriptors, but I was surprised by following behaviour:

from attr import attributes, attr
@attributes
class A(object):
    a = attr()
@attributes
class B(A):
    b = attr()
@attributes
class C(B):
    c = attr()

raises a syntax error:

Traceback (most recent call last):
  File "yo.py", line 15, in <module>
    class C(B):
  File "/home/davidc/.envs/jaguar-dev/local/lib/python2.7/site-packages/attr/_make.py", line 194, in attributes
    return wrap(maybe_cl)
  File "/home/davidc/.envs/jaguar-dev/local/lib/python2.7/site-packages/attr/_make.py", line 186, in wrap
    cl = _add_init(cl)
  File "/home/davidc/.envs/jaguar-dev/local/lib/python2.7/site-packages/attr/_make.py", line 340, in _add_init
    bytecode = compile(script, unique_filename, "exec")
  File "<attrs generated init 24e3b3b777d1b457ffb869223ee4a4b7665529ed>", line 1
SyntaxError: duplicate argument 'a' in function definition

So it looks like one level of inheritance works (B works as expected), but not multiple.

[hynek]

Congratulations, you found the first bug in attrs. :)

[hynek]

If you could verify your issue is fixed I’d roll 15.1.0. Thanks!

[cournape]

Looks like it works ! Thanks for the prompt fix

[hynek]

(I have to correct myself: the first bug in a released version. the first bug overall was found by @econchick in #5, mea culpa ;))