- cattrs version: 0.40
- Python version: 3.6.2
- Operating System: Ubuntu 16.04 x86_64
Description
The attrs package allows default values for any given field, and allows initialisation of an attrs class without keys for which a default was provided.
With the following definition,
@attr.s(slots=True, frozen=True)
class Cfg(object):
a = typed(int)
b = typed(Optional[int])
c = attr.ib(convert=int, default=7)
d = typed(Optional[int], default=5)
We can instantiate a Cfg object as:
In [243]: Cfg(**dt)
Out[243]: Cfg(a=5, b=None, c=7, d=5)
When used with cattr.structure, however, the default values seem to be entirely ignored, moreover there is a KeyError exception thrown. While wrapping the attr.ib type in an Optional avoids the error, we wind up with None instead of the provided default value.
cattr.structure_attrs_fromdict({'a':5,'b':None}, Cfg)
In [208]: cattr.structure_attrs_fromdict(dt, Cfg)
---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
<ipython-input-208-5adc18822e6a> in <module>()
----> 1 cattr.structure_attrs_fromdict(dt, Cfg)
~/dev/survey_stats/venv/lib/python3.6/site-packages/cattr/converters.py in structure_attrs_fromdict(self, obj, cl)
255 name = a.name
256 # We detect the type by metadata.
--> 257 converted = self._structure_attr_from_dict(a, name, obj)
258 conv_obj[name] = converted
259
~/dev/survey_stats/venv/lib/python3.6/site-packages/cattr/converters.py in _structure_attr_from_dict(self, a, name, mapping)
265 if type_ is None:
266 # No type.
--> 267 return mapping[name]
268 if isinstance(type_, _Union):
269 # This is a union.
KeyError: 'c'
In [249]: cattr.structure_attrs_fromdict({'a':5,'b':None, 'c':3}, Cfg)
Out[249]: Cfg(a=5, b=None, c=3, d=None)
Description
The attrs package allows default values for any given field, and allows initialisation of an attrs class without keys for which a default was provided.
With the following definition,
We can instantiate a Cfg object as:
When used with cattr.structure, however, the default values seem to be entirely ignored, moreover there is a KeyError exception thrown. While wrapping the attr.ib type in an Optional avoids the error, we wind up with None instead of the provided default value.