[Numpy-discussion] Py-API: Deprecate `np.dtype(np.floating)` and similar dtype creation

[Nathan]

Yeah, that seems to be more popular:

https://github.com/search?q=%22dtype%3Dnp.integer%22&type=Code

On Fri, Feb 14, 2020 at 2:45 PM Sebastian Berg <sebastian at sipsolutions.net>
wrote:

> On Fri, 2020-02-14 at 14:39 -0700, Nathan wrote:
> > For what it's worth, github search only finds two instances of this
> > usage:
> >
> > https://github.com/search?q=%22np.dtype%28np.floating%29%22&type=Code
> >
>
> In most common thing I would expect to be `dtype=np.integer` (possibly
> without the `dtype` as a positional argument).
> The call your search finds is nice because it must delete `np.dtype`
> call.
> As is, it is doing the incorrect thing so the deprecation would flush
> out a bug.
>
> - Sebastian
>
>
> > On Fri, Feb 14, 2020 at 2:28 PM Sebastian Berg <
> > sebastian at sipsolutions.net> wrote:
> > > Hi all,
> > >
> > > In https://github.com/numpy/numpy/pull/15534 I would like to start
> > > deprecating creating dtypes from "abstract" scalar classes, such
> > > as:
> > >
> > > np.dtype(np.floating) is np.dtype(np.float64)
> > >
> > > While, at the same time, `isinstance(np.float32, np.floating)` is
> > > true.
> > >
> > > Right now `arr.astype(np.floating, copy=False)` and, more
> > > obviously,
> > > `arr.astype(np.dtype(np.floating), copy=False)` will cast a float32
> > > array to float64.
> > >
> > > I think we should deprecate this, to consistently enable that in
> > > the
> > > future `dtype=np.floating` may choose to not cast a float32 array.
> > > Of
> > > course for the `astype` call the DeprecationWarning would be
> > > changed to
> > > a FutureWarning before we change the result value.
> > >
> > > A slight (but hopefully rare) annoyance is that `np.integer` might
> > > be
> > > used since it reads fairly well compared to `np.int_`. The large
> > > upstream packages such as SciPy or astropy seem to be clean in this
> > > regard, though (at least almost clean).
> > >
> > > Does anyone think this is a bad idea? To me these deprecations seem
> > > fairly straight forward, possibly flush out bugs/unintended
> > > behaviour,
> > > and necessary for consistent future behaviour. (More similar ones
> > > may
> > > have to follow).
> > >
> > > If there is some, but not much, hesitation, I can also add this to
> > > the
> > > NEP 41 draft. Although I currently feel it is the right thing to do
> > > even if we never had any new dtypes.
> > >
> > > - Sebastian
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