[SciPy-Dev] factorial2 does not return a float with exact=False

David Goldsmith d.l.goldsmith@gmail....
Mon Jun 28 23:56:05 CDT 2010


On Mon, Jun 28, 2010 at 9:37 PM, Vincent Davis <vincent@vincentdavis.net>wrote:

> On Mon, Jun 28, 2010 at 10:34 PM, Skipper Seabold <jsseabold@gmail.com>
> wrote:
> > On Mon, Jun 28, 2010 at 11:14 PM, David Goldsmith
> > <d.l.goldsmith@gmail.com> wrote:
> >>
> >> On Mon, Jun 28, 2010 at 6:29 PM, Vincent Davis <
> vincent@vincentdavis.net> wrote:
> >>>
> >>> On Mon, Jun 28, 2010 at 7:24 PM, Warren Weckesser
> >>> <warren.weckesser@enthought.com> wrote:
> >>> > Vincent Davis wrote:
> >>> >> On Mon, Jun 28, 2010 at 7:11 PM, Vincent Davis <
> vincent@vincentdavis.net> wrote:
> >>> >>
> >>> >>> According to the docs factorial2 should return a float or int,
> float
> >>> >>> in the case of exact=False, It does not.
> >>> >>>
> >>> >>>
> >>> >>>>>> import scipy.misc.common as sc
> >>> >>>>>> sc.factorial2(7, exact=False)
> >>> >>>>>>
> >>> >>> array(105.00000000000001)
> >>> >>>
> >>> >>>>>> sc.factorial2(7, exact=True)
> >>> >>>>>>
> >>> >>> 105L
> >>> >>>
> >>> >>>>>> sc.factorial2(8, exact=True)
> >>> >>>>>>
> >>> >>> 384L
> >>> >>>
> >>> >>>>>> sc.factorial2(8, exact=False)
> >>> >>>>>>
> >>> >>> array(384.0)
> >>> >>>
> >>> >>>>>> sc.factorial2(8, exact=False)
> >>> >>>>>>
> >>> >>
> >>> >> Same with factorial
> >>> >>
> >>> >>
> >>> >>>>> sc.factorial(5, exact=False)
> >>> >>>>>
> >>> >> array(120.0)
> >>> >>
> >>> >>>>> arr = np.array([3,4,5])
> >>> >>>>> sc.factorial(arr, exact=False)
> >>> >>>>>
> >>> >> array([   6.,   24.,  120.])
> >>> >>
> >>> >>>>> sc.factorial(5, exact=True)
> >>> >>>>>
> >>> >> 120L
> >>> >>
> >>> >
> >>> > I think the problem is simply that it is an awkward API.  After
> looking
> >>> > at the code for factorial, a more precise description is:
> >>> >
> >>> > If `exact` is True, `n` must be an integer, and an integer is
> returned.
> >>> >
> >>> > If `exact` is False, `n` is array_like, and an array the same shape
> as
> >>> > `n` is returned.
> >>>
> >>> I am finding that when editing the docs it is not always clear if the
> >>> problem is the docs or the function.
> >>> comb() has a similar issue.
> >>>
> >>> I guess my question is?
> >>> My thought is the you factoral(), or comb() return an array only if 1,
> >>> exact=False and n is not an array. Basically you get back the same
> >>> dtype as input.
> >>> That said fixing the docs is just a little easier.
> >>
> >> This issue has come up many times; again, here's the "policy": document
> desired/intended behavior, not actual behavior - if they differ, and the doc
> specifies the desired/intended behavior correctly, then file a (code) bug
> report; if the function is behaving correctly, but the doc doesn't correctly
> document that behavior, correct the doc in the Wiki; if both are wrong (and
> there is precedent for this) then both actions must be taken.  What is the
> implication of this when you encounter this situation while editing the
> docs?  You must do what you've done: post to the appropriate list, asking
> which is correct, and wait a little while for a decision; if several days
> pass and no one responds, re-post; if several days pass and there remains
> disagreement on the matter, file a bug ticket, so the debate moves over
> there and "move on."
> >>
> >
> > Sound good?
> >
> >
> http://docs.scipy.org/numpy/Questions+Answers/#documented-and-actual-behavior-differ
>
> So whats the desired/intended behavior? i.e. go with what Warren
> proposed for the docs or what I proposed for the behavior?
>

This is where you play that waiting game for a bit: you can't count on
everyone who has an opinion on the matter (and let's face it: some people's
opinions matter more than others in this community, e.g., "when RK speaks,
people listen") to have seen this so soon.  Wait a few days, then ask again
(if necessary).

DG

>
> Vincent
>
> >
> > Skipper
> > _______________________________________________
> > SciPy-Dev mailing list
> > SciPy-Dev@scipy.org
> > http://mail.scipy.org/mailman/listinfo/scipy-dev
> >
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-- 
Mathematician: noun, someone who disavows certainty when their uncertainty
set is non-empty, even if that set has measure zero.

Hope: noun, that delusive spirit which escaped Pandora's jar and, with her
lies, prevents mankind from committing a general suicide.  (As interpreted
by Robert Graves)
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