fraction in nested list comprehension

[Makoto Yamashita]

Hi,

I noticed that fractions in nested list comprehensions are apparently interpreted in the Python way. So, with the input

[[j/k for j in range(1,k+1)] for k in range(1,5)]

I get

[[1], [0, 1], [0, 0, 1], [0, 0, 0, 1]] .

With a single level there's no such issue: [j/3 for j in range(1,4)] returns [1/3, 2/3, 1] .

For now I'm dealing with it by enclosing the variables in Integer(). Is there any better solution?

thanks,

Makoto

[William Stein]

This is pretty much *the* worst gotcha of Sage.   You could do this instead:

[[j/k for j in srange(1,k+1)] for k in srange(1,5)]

It makes a range-like object, but respects the types of the input variables of the srange, which are Integer in this case. 

 -- William

 

thanks,

Makoto

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[Makoto Yamashita]

I see, it did work indeed. Thanks!

Makoto

[kcrisman]

This is pretty much *the* worst gotcha of Sage.   You could do this instead:

[[j/k for j in srange(1,k+1)] for k in srange(1,5)]

It makes a range-like object, but respects the types of the input variables of the srange, which are Integer in this case. 

Yup, this is always nasty.  Now, with Python 3 this *sort* of goes away, but am I correct that j/k will then give (floating point) 0.5, not a Rational Sage type, right?  So in some sense this will still be an issue, just a different one.