[Numpy-discussion] ufunc oddities

Charles R Harris charlesr.harris@gmail....
Sat May 24 21:09:06 CDT 2008


On Sat, May 24, 2008 at 7:47 PM, Robert Kern <robert.kern@gmail.com> wrote:

> On Sat, May 24, 2008 at 8:31 PM, Charles R Harris
> <charlesr.harris@gmail.com> wrote:
> > Hi All,
> >
> > I'm writing tests for ufuncs and turned up some oddities:
> >
> > In [4]: degrees(True)
> > Out[4]: 57.29578
> >
> > In [5]: radians(True)
> > Out[5]: 0.017453292
> >
> > In [6]: sin(True)
> > Out[6]: 0.84147096
> >
> > Do we want numeric functions to apply to booleans?
>
> I don't see a good reason to prevent it. They are just 0 and 1 under
> the covers and behave like it everywhere else (e.g. True + True == 2
> and the very useful boolean_mask.sum()).
>

True + True == 1

In [5]: x + x
Out[5]: array([ True,  True], dtype=bool)

In [6]: (x + x).astype(int)
Out[6]: array([1, 1])

That is how the inner loop is implemented.

Chuck
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