On 07/02/2016 07:46 AM, Jonathan Underwood wrote:
Hi,
As documented, the default constructor for objects that inherit from
Base doesn't work in multiple inheritance situations (unless Base is
last in the list of classes, I suppose). It wouldn't be too difficult to
change this without breaking existing expectations, I believe. Something
like this:
def _declarative_constructor(self, **kwargs):
"""A simple constructor that allows initialization from kwargs. Sets
attributes on the constructed instance using the names and values
in ``kwargs``.
Differs from the default constructor in that (a) keys not present
in the attributes of the instance's class are ignored; (b) we call
super at the end to ensure proper multiple inheritance behaviour.
"""
cls_ = type(self)
unused_kwargs = dict()
for k in kwargs:
if hasattr(cls_, k):
setattr(self, k, kwargs[k])
else:
unused_kwargs.update({k:kwargs[k]})
super(Base, self).__init__(**unused_kwargs)
Well, all existing tests would have to pass, but also I wonder where are
you getting "Base" above? It's not present and would have to be passed
to an enclosing function that generates a _declarative_constructor as a
closure. That would imply a change in the API of the declarative_base
function, which accepts a constructor function as an argument, to now
accept a constructor-generating function.
This plays well with other classes, and still raises a TypeError
exception if there are kwargs specified which are not used in the MRO.
Would a pull request implementing this be accepted? I did have a look
around but didn't find previous discussion of this issue, but apologies
if I missed something.
Best wishes,
Jonathan.
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