[Numpy-discussion] Re: Giving deprecation of e.g. `float(np.array([1]))` a shot (not 0-d)

April 20, 2023

      On 4/20/23, Sebastian Berg <sebastian@sipsolutions.net> wrote:
...
Hi all,
Unlike conversions of 0-d arrays via:
float(np.array([1]))
conversions of 1-D or higher dimensional arrays with a single element
are a bit strange:
float(np.array([1]))
And deprecating it has come up often enough with many in favor, but
also many worried about the possible annoyance to users.
I decided to give the PR a shot, I may have misread the room on it
though:
https://github.com/numpy/numpy/pull/10615
So if this turns out noisy (or you may simply disagree), I am happy to
revert!
There was always the worry that it might be painful for downstream.
SciPy, pandas, matplotlib should all be fine (were fixed in the past
years).  And the fact that SciPy required much more changes than the
other gives me some hope that many libraries won't mind.
For end-users, I would lean towards taking it slow, but if you see
issues there we can also revert of course.
Cheers,
Sebastian
Thanks Nico, and Sebastian, and everyone else involved in the PRs.

This also affects `np.float64`:

```
In [61]: np.__version__
Out[61]: '1.25.0.dev0+1203.g1acac891f'

In [62]: np.float64(0.0)
Out[62]: 0.0

In [63]: np.float64(np.array(0.0))
Out[63]: 0.0

In [64]: np.float64(np.array([0.0]))
<ipython-input-64-0f0309f2cf0c>:1: DeprecationWarning: Conversion of
an array with ndim > 0 to a scalar is deprecated, and will error in
future. Ensure you extract a single element from your array before
performing this operation. (Deprecated NumPy 1.25.)
  np.float64(np.array([0.0]))
Out[64]: 0.0

In [65]: np.float64(np.array([0.0, 0.0]))
Out[65]: array([0., 0.])

```

In 1.24.2, `np.float64(np.array([0.0])` returns the the scalar 0.0.

If passing arrays to `np.float64()` is intentionally supported, it
seems it would be more consistent for `np.float64(np.array([0.0]))` to
return `np.array([0.0])`.  That is how the other numpy types work
(e.g. `np.complex128`, `np.int64`, etc.). But I'm not sure if there is
a deprecation/update path that would get us there.

Warren
...
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[Numpy-discussion] Re: Giving deprecation of e.g. `float(np.array([1]))` a shot (not 0-d)

Warren Weckesser