[Numpy-discussion] random.uniform documentation bug?
David Goldsmith
d.l.goldsmith@gmail....
Tue Feb 23 13:39:16 CST 2010
On Tue, Feb 23, 2010 at 11:25 AM, Robert Kern <robert.kern@gmail.com> wrote:
> On Tue, Feb 23, 2010 at 13:05, David Goldsmith <d.l.goldsmith@gmail.com>
> wrote:
> > 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),
>
> <shudder>
>
> > but
> > does everyone agree (or at least not block) that this is acceptable
> > behavior?
>
> It's a useful feature. Whenever there is a low/high pair of arguments,
> a user frequently has to write code like so:
>
> low, high = min(a, b), max(a, b)
>
> just to satisfy the argument spec of the function. This function does
> not really require knowing which is which for its implementation, so
> requiring them to be one way is simply arbitrariness for the sake of
> arbitrariness.
>
OK.
> > 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. ;-)
>
> So do it. But please, don't use frightening terminology like you are
> here. Just state the fact clearly and succinctly as in the
> random.uniform() docs.
>
Aw shucks, these docstrings are so dry. (Just kidding.) ;-)
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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