There is an `nsimplify` function that you can link up to a function that
will change floats to Rationals:
def nrat(e, maxden=10):
f = e.atoms(Float)
reps = {}
for i in f:
r = nsimplify(i, rational=True)
if r.q <= maxden: reps[i] = r
return e.xreplace(reps)
>>> nrat(1/2 + 13/17*x)
0.764705882352941*x + 1/2
>>> nrat(1/2 + 13/17*x, 20)
13*x/17 + 1/2
>>> nrat(x**(1/2))
sqrt(x)
/c
On Saturday, May 15, 2021 at 11:43:13 PM UTC-5 asme...@gmail.com wrote:
> On Sat, May 15, 2021 at 3:02 PM David Bailey <da...@dbailey.co.uk> wrote:
> >
> > On 14/05/2021 23:01, Oscar Benjamin wrote:
> >
> > That's a great video but it's describing something very different. There
> he types exact input into the calculator and then calculator somehow makes
> a numeric/symbolic approximation that goes wrong. I'm not talking about
> changing anything for exact input. I'm only referring to the first step of
> passing a float to sympy. Maybe we need a more limited version of nsimplify
> for this. I can certainly see the reasons for not trying to convert float
> to Rational but I can also see how much of a problem it is for users. The
> "power users" will not have so much of a problem converting their input to
> Float if that's what they meant.
> >
> >
> > Yes, but surely that would just lead to a new set of anomalies because
> the float has finite precision. I mean it would be possible to translate
> floats back into fractions for simple fractions like 3/4, but what about
> 123456789123456788/123456789123456789? Also, people sometimes pass
> intentional floats to SymPy without being power users!
> >
> > Wouldn't it be possible to persuade the Python team to implement
> auto_int_to_Integer outside of IPython - it can't be hard to do?
>
> My argument is that it's really only a good idea to do this in an
> interactive environment. In that case, you are probably using
> something like IPython or Jupyter notebook.
>
> It would in theory be possible to make it work in a Python script
> using a codec trick
> (https://rahul.gopinath.org/post/2019/12/25/python-macros/). At that
> point, you are more or less creating your own DSL.
>
> For any kind of upstream change to Python itself, you have to remember
> that 99% of Python users don't want this feature. So you'd have to
> implement it in a way that doesn't affect them.
>
> Aaron Meurer
>
> >
> > David
> >
> >
> >
> >
> > --
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> https://groups.google.com/d/msgid/sympy/c7fa2c5f-b7c3-4e2d-bbfd-29b8ad81e553%40dbailey.co.uk
> .
>
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