Default value is being ignored while structuring the attr class

[shwetas1205]

• cattrs version: 0.5.0
• Python version: 3.6.2
• Operating System: Debian GNU/Linux 8.9 (jessie)

Description

When I am trying use structure on an attr class having default values set for few optional attributes, those default values are being ignored and not returning to returned object

What I Did

Here is the sample code:

import attr
from cattr import structure, typed
from typing import Optional


@attr.s
class A(object):
    a = typed(Optional[int], default=0)

@attr.s
class B(object):
    b = attr.ib(validator=optional(instance_of(int)), default=0)

When I tried structure({}, A) I expected A1(a=0) but I get A1(a=None)
Similarly for structure({}, B) I get following error

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/xxx/cattr/converters.py", line 171, in structure
    return self.structure_func.dispatch(cl)(obj, cl)
  File "/xxx/cattr/converters.py", line 86, in <lambda>
    lambda *args, **kwargs: self.structure_attrs(*args, **kwargs))
  File "/xxx/cattr/converters.py", line 276, in structure_attrs_fromdict
    converted = self._structure_attr_from_dict(a, name, obj)
  File "/xxx/cattr/converters.py", line 286, in _structure_attr_from_dict
    return mapping[name]
KeyError: 'b'

A fix something like will fix the issue: shwetas1205@7d6d6fa

[Tinche]

Hi! This is a duplicate of #10 I think. It's something I will look at after attrs 17.3 is released and I do another development pass of cattrs. Thanks for your interest :)

[shwetas1205]

Oops, I think I missed #10 Thanks for pointing that out.

I wanted this support for one of my work so I went ahead added a fix here: https://github.com/Tinche/cattrs/pull/15 it would be great if you could have a look. Thanks :)