> On 14 Oct 2019, at 21:55, DL Neil via Python-list <python-list@python.org>
> wrote:
>
> Is there a technique or pattern for taking a (partially-) populated instance
> of a class, and re-creating it as an instance of one of its sub-classes?
The pattern I know is to use a factory function to choose between a number of
concrete classes based on some information.
In this case it seems that after collecting enough information you could create
such a class.
The other thought is to have the classes support a method that returns a
"better" class.
x.setProp(...)
x = x.upgradeInstance()
I have seen code that messes around with __class__ but I think that its a
maintenance issue to do that.
Apart from the person who writes that code would have a clue what it's doing.
Barry
>
>
> In a medically-oriented situation, we have a Person() class, and start
> collecting information within an instance (person = Person(), etc).
>
> During the data-collection process the person's sex may become obvious, eg
> few males have become/been pregnant.
>
> We could stick with Person() and implement specific methods therein, rather
> than separate Man and Woman sub-classes, but...
>
> It seemed better (at the design-level) to have Man( Person ) and Woman(
> Person ) sub-classes to contain the pertinent attributes, source more
> detailed and specific questions, and collect such data; by gender.
>
> In coding-practice, once gender becomes apparent, how should the instance of
> the Man() or Woman() sub-class be created - and established with the ID and
> other attributes previously collected as a Person instance?
>
> This attempt seems hack-y:
>
> man = Man()
> man.__dict__.update( person.__dict__ )
>
>
> Is there a pythonic tool for such, or is the task outlined
> fundamentally-inappropriate?
>
> --
> Regards,
> =dn
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>
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