Ah great! Didn't think of that. Thanks!
Yeah, once my current pull request is done
(https://github.com/sympy/sympy/pull/2829)
I might try to find some time to dig around with the metaclasses (I'm not
the biggest fan
of metaclasses in general - I usually find them quite confusing in practice)
Best regards
/Björn
On Wednesday, 29 January 2014 05:04:45 UTC+1, Aaron Meurer wrote:
>
> When you define a class inside a function, every time the function is
> run, you get a new class, which will compare unequal to any previous
> versions (the same thing is true when you define a function within a
> function by the way). You could cache the class instances, but to me,
> it seems easier to just set the option in the __init__ method of the
> class. Something like
>
> class MaybeRealFunction(UndefinedFunction):
> def __init__(self, *args, **kwargs):
> self.real = kwargs.pop('real')
> super(MaybeRealFunction, self).__init__(*args, **kwargs)
>
> @staticmethod
> def _eval_is_real(self):
> return self.real
>
> In [104]: r1 = MaybeRealFunction('f', real=False)
>
> In [105]: r2 = MaybeRealFunction('f', real=False)
>
> In [106]: r1(x) == r2(x)
> Out[106]: True
>
> In [107]: r1(x).is_real
> Out[107]: False
>
> But also note that:
>
> In [108]: r3 = MaybeRealFunction('f', real=True)
>
> In [109]: r2(x) == r3(x)
> Out[109]: True
>
> If real is the only assumption you care about, you should just create
> two separate classes, RealFunction and NotRealFunction. Otherwise,
> you'll need override _hashable_content so that the hash (and therein
> equality) comes out different. You noted that you are using them as
> keys in dictionaries, so probably you do care about this.
>
> By the way, it would be nice if Function supported this directly,
> i.e., Function('f', real=False). If you don't mind actually digging
> into the metaclasses, a pull request would nice.
>
> Aaron Meurer
>
>
> On Tue, Jan 28, 2014 at 10:16 AM, Björn Dahlgren
> <bjo...@gmail.com<javascript:>>
> wrote:
> > Hello!
> >
> > I have an application where I use undefined functions as keys in
> > dictionaries.
> >
> > This works great out of the box for sympy.Function
> > However, I want to set real=True so I created a class factory which
> > overrides _eval_is_real
> >
> > Now the trouble starts. I tried to work my way through the jungle of
> > metaclasses and the assumptions systems
> > but I don't seem to be able to fix this:
> >
> > -*- coding: utf-8 -*-
> >
> > from sympy.core.function import UndefinedFunction
> > import sympy
> >
> > def MaybeRealFunction(key, real=None):
> >
> > class _Function(UndefinedFunction):
> > @staticmethod
> > def _eval_is_real(self):
> > return real
> >
> > return _Function(key)
> >
> >
> > def main():
> > x = sympy.Symbol('x')
> > assert x == sympy.Symbol('x')
> >
> > f_x = sympy.Function('f')(x)
> > assert f_x == sympy.Function('f')(x)
> >
> > g_x = MaybeRealFunction('g', real=True)(x)
> > assert g_x.is_real
> > assert g_x == g_x
> > assert g_x == MaybeRealFunction('g', real=True)(x) # <--- This one
> fails
> >
> > if __name__ == '__main__':
> > main()
> >
> >
> > Any ideas?
> >
> > Best regards,
> > /Björn
> >
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