Le lundi 21 décembre 2015 17:32:03 UTC+1, Mark Bell a écrit :
>
> The __invert__ methods, which controls the behaviour of the ~ operator, of
> Integers and ints are different.
>
> In Python, for an int x, its invert ~x is defined to be its two's
> complement and is given by -1-x
> <https://wiki.python.org/moin/BitwiseOperators>.
>
> On the other hand, in Sage for an Integer x
> (from sage.rings.integer.Integer), its __invert__ is defined to be 1 / x
> <https://github.com/sagemath/sage/blob/master/src/sage/rings/integer.pyx#L5999-L6011>
> .
>
> Unfortunately this difference means that ~x different results in Sage and
> Python and so is causing some of my scripts and packages that run under
> Python to break under Sage. Most notably, that under Sage ~0 raises a
> "ZeroDivisionError: Rational division by zero" error rather than returning
> -1.
>
> Looking through the git history it appears that this has been the
> convention since at least October 2006
> <https://github.com/sagemath/sage/blob/b94db547579596d7979e28aa9aff1cdb45193bcc/src/sage/rings/integer.pyx#L1590-L1593>.
>
> Is there a reason why __invert__ was chosen to act this way rather than
> match the Python convention?
>
maybe because :
sage: var("x")
x
sage: ~x
1/x
sage: var("a,b,c,d")
(a, b, c, d)
sage: M=matrix([[a,b],[c,d]])
sage: ~M
[1/a - b*c/(a^2*(b*c/a - d)) b/(a*(b*c/a - d))]
[ c/(a*(b*c/a - d)) -1/(b*c/a - d)]
were deemed useful ?
HTH,
--
Emmanuel Charpentier
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