Decimal to fraction?

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There are at least three ways to recover a rational from one of its numerical approximations:

sage: a = .1/8
sage: a.simplest_rational()
1/80
sage: a.nearby_rational(0.0001)
1/80
sage: a.exact_rational()
3602879701896397/288230376151711744

You can have a look to their respective documentations to see the differences. And you should understand that the floating point number a is not equal to 1/80 but to 3602879701896397/288230376151711744 !

Dupe of http://ask.sagemath.org/question/2758...

I've posted an alternate answer to the question at the link above. The basic answer: I ran across another way that's posted here where the author, John D Cook mentions the nsimplify command in SymPy (which you can can access in Sage). Here's nsimplify in action with your example