You could try using the evaluate=False flag in Mul:
In [4]: Mul(2, S(1)/4, evaluate=False)
Out[4]:
2
─
4

Aaron Meurer
On Aug 6, 2009, at 3:43 PM, James Pearson wrote:

> I'm working on an online homework system, where I'm using SymPy to  
> store data, as well as do all of the hard calculations when a test  
> for equality is needed.  This ends up being a far more basic usage  
> of the library than most people here, it seems, from reading over  
> the list.
>
> One thing that I'm having trouble with is in storing equation,  
> fractions, or other mathy things.  For instance, perhaps I have the  
> fraction 6/4; if I create a Rational out of it, it becomes 3/2,  
> which is particularly unfortunate if the question asks the student  
> to reduce the fraction!  I could store it as a string, but I like  
> being able to use it as a sympy object, in particular, feeding it to  
> printing.latex.  A similar thing happens with equations; all of the  
> menial work that is exactly what I'm trying to test gets done  
> automagically by sympy.
>
> What would you suggest?  Would subclassing Rational (and other  
> appropriate classes) be the best way to get the behavior I want?
>
> Thanks for all of the work on this library, btw.  I thought I was  
> going to have to write reduction and latex-generation functions  
> myself.  Silly me should have learned by now that there's a Python  
> library (or 2 or 3) for everything.
>
> --
> James Pearson
> --
> The best way to predict the future is to invent it.
>  - Alan Kay
>
> >


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