[Python-ideas] Quick idea: defining variables from functions that take the variable name

[Sven R. Kunze]

On 01.06.2016 21:48, Michael Selik wrote:
> On Wed, Jun 1, 2016 at 3:14 PM Sven R. Kunze <srkunze at mail.de 
> <mailto:srkunze at mail.de>> wrote:
>
>     On 01.06.2016 18:24, Michael Selik wrote:
>>     I don't see how that would be improved by a special syntax for
>>     the [RHS] to know the identifier it's being assigned to. Could
>>     you clarify that?
>     I was referring to the issue that fields don't know neither their
>     containing form classes nor their form instances. In some
>     circumstances, one need to do that in order to correctly work with
>     the field (think of the prefix of the form which needs to be
>     reflected in the field but there are more missing pieces of
>     information).
>
>     As mentioned to Steven, in this case the name does not suffices at
>     all. So, I am not sure how to handle this right now. This might
>     belong to a greater issue of referring back which currently needs
>     to be handled manually in all cases.
>
>
> I always find bi-directional has-a relationships to be troublesome. If 
> it were necessary frequently, I'd expect the Form metaclass to loop 
> over the declared_fields and set some .form attribute to the 
> new_class. Django is way too big for me to grok from light reading, so 
> I won't presume to understand the choices made there.
>
> https://github.com/django/django/blob/master/django/forms/forms.py#L27

That would be a hand-made solution and would work quite efficiently in 
terms of productivity for Django projects.

Recently, I started a private side project where I would need that 
back-relationship as well. This time, it's about rigid body simulation 
where I would like to pick a point in body space of a body and always 
get the correct world space coordinates when accessing. Same thing, but 
also hand-made by myself and it requires special attention from time to 
time.

I don't say I have a nice, readable solution for this but it seems to me 
that *providing context* to Python objects would as much help as it 
helps Google to provide extremely accurate search results.


Best,
Sven


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