[Tutor] Little problem with math module
John Fouhy
john at fouhy.net
Mon Apr 21 04:52:54 CEST 2008
On 21/04/2008, John Fouhy <john at fouhy.net> wrote:
> >>> -1 ** (1.0/2.0)
> -1.0
Replying to myself:
It turns out that all is not what it seems. Let's try again:
>>> (-1)**0.5
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: negative number cannot be raised to a fractional power
So, to revise my answer, for math.pow(x,y) or x**y, python will refuse
negative values of x. This might not be mathematically perfect, but
you get what you pay for, I guess.
Furthermore, python evaluates "-x**y" as "-(x**y)" which is why it
seemed to give correct answers.
--
John.
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