[Numpy-discussion] random.uniform documentation bug?

David Goldsmith d.l.goldsmith@gmail....
Tue Feb 23 13:05:37 CST 2010


On Tue, Feb 23, 2010 at 10:29 AM, Robert Kern <robert.kern@gmail.com> wrote:

> On Tue, Feb 23, 2010 at 08:21, Alan G Isaac <aisaac@american.edu> wrote:
> > This behavior does not match the current documentation.
> >
> >>>> np.random.uniform(low=0.5,high=0.5)
> > 0.5
> >>>> np.random.uniform(low=0.5,high=0.4)
> > 0.48796883601707464
> >
> > I assume this behavior is intentional and it is
> > the documentation that is in error (for the case
> > when high<=low)?
>
> Well, the documentation just doesn't really address high<=low. In any
> case, the claim that the results are in [low, high) is wrong thanks to
> floating point arithmetic. It has exactly the same issues as the
> standard library's random.uniform() and should be updated to reflect
> that fact:
>
> random.uniform(a, b)
>  Return a random floating point number N such that a <= N <= b for a
> <= b and b <= N <= a for b < a.
>
>  The end-point value b may or may not be included in the range
> depending on floating-point rounding in the equation a + (b-a) *
> random().
>
>
> We should address the high < low case in the documentation because
> we're not going to bother raising an exception when high < low.
>

Well, an exception isn't the only option (e.g., it could return NaN), but
does everyone agree (or at least not block) that this is acceptable
behavior?  IMO, if this function is going to allow high < low, then the doc
should _also_ be _quite_ clear that if this "feature" might mess up the
user's program in some way, then the user will have to implement their own
safeguard against such parameters being fed to the monster. ;-)

DG


>
> --
> Robert Kern
>
> "I have come to believe that the whole world is an enigma, a harmless
> enigma that is made terrible by our own mad attempt to interpret it as
> though it had an underlying truth."
>  -- Umberto Eco
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