Perhaps it is also worth going back to explore our original motivation for
making this change.
One reason was that Sebastian didn't like people doing `x.shape = ...`. Users
do that, presumably, to trigger an error if a copy needs to be made. However,
we can catch that already:
x = np.reshape(y, ...)
if np.may_share_memory(x, y):
...
We can fix Sebastian's issue by introducing a `copy` keyword to `reshape`,
which currently has none:
x = np.reshape(y, copy='never')
For consistency, it would be nice to have `np.array` support copy=never, but if
there is no urgency we can take the long route towards an API that uses strings
(consistent with the rest of NumPy).
The arguments against string names *right now* is that, if users write code
with `copy='if-needed'` it will not work correctly with old NumPy code, since
old versions will evaluate `if-needed` to True. The assessment was that this
happens frequently, but we should consider how frequently, and how big of an
issue it is.
So, I guess ultimately I am wondering if the change to `np.array` is needed
right now, or whether we can get away without it for a while.
Stéfan
On Tue, Jun 22, 2021, at 15:21, bas van beek wrote:
> > Stefan, that sketch is more complicated than it needs to be - `np.copy` is
> > a python function, so you can just attach the attributes directly!
> > (although maybe there are implications for static typing)
>
> For the type annotations we can simply use something akin to Stéfans proposed
> `NpCopy` class;
> probably in combination with `Protocol`.
> It's a bit more work compared to annotating a normal python function, but
> it's quite easy nevertheless.
>
> Regards, Bas
>
>
> *From:* NumPy-Discussion
> <numpy-discussion-bounces+bas.vanbeek=hotmail....@python.org> on behalf of
> Eric Wieser <wieser.eric+nu...@gmail.com>
> *Sent:* 21 June 2021 18:56
> *To:* Discussion of Numerical Python <numpy-discussion@python.org>
> *Subject:* Re: [Numpy-discussion] copy="never" discussion and no deprecation
> cycle?
>
>
> Stefan, that sketch is more complicated than it needs to be - `np.copy` is a
> python function, so you can just attach the attributes directly! (although
> maybe there are implications for static typing)
> ```
> class CopyFlag(enum.Enum):
> IF_NEEDED = 0
> ALWAYS = 1
> NEVER = 2
>
> np.copy.IF_NEEDED = CopyFlag.IF_NEEDED
> np.copy.ALWAYS = CopyFlag.ALWAYS
> np.copy.NEVER = CopyFlag.NEVER
> ```
> It would also work nicely for the `True/False/other` version that was
> proposed in the much older PR as `np.never_copy`:
> ```
> class _CopyNever:
> def __bool__(self): raise ValueError
>
> np.copy.NEVER = _CopyNever()
> ```
>
> All of these versions (and using the enum directly) seem fine to me.
> If we go down the enum route route, we probably want to add "new-style"
> versions of `np.CLIP` and friends that are true enums / live within a more
> obvious namespace.
>
> Eric
>
> On Mon, 21 Jun 2021 at 17:24, Stefan van der Walt <stef...@berkeley.edu>
> wrote:
>> On Sun, Jun 20, 2021, at 20:46, Gagandeep Singh wrote:
>> > I have recently joined the mailing list and have gone through the previous
>> > discussions on this thread. I would like to share my analysis (advantages
>> > and disadvantages) of three possible alternatives (Enum, String, boolean)
>> > to support the proposed feature.
>>
>> Thanks for this thorough analysis, Gagandeep!
>>
>> I'll throw one more heretical idea out there:
>>
>> `np.copy.IF_NEEDED`, `np.copy.ALWAYS`, `np.copy.NEVER`.
>>
>> This has the advantages of the enum, doesn't pollute the global namespace,
>> and has an intuitive name.
>>
>> `np.array(x, copy=np.copy.ALWAYS)`
>>
>> It would be slightly more awkward to type, but is doable. A rough Python
>> version sketch would be:
>>
>> class CopyFlag(enum.Enum):
>> IF_NEEDED = 0
>> ALWAYS = 1
>> NEVER = 2
>>
>> class NpCopy:
>> IF_NEEDED : CopyFlag = CopyFlag.IF_NEEDED
>> ALWAYS : CopyFlag = CopyFlag.ALWAYS
>> NEVER : CopyFlag = CopyFlag.NEVER
>>
>> def __call__(self, x):
>> return ...whatever copy returns...
>>
>> np.copy = NpCopy()
>>
>>
>> Stéfan
>> _______________________________________________
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>> NumPy-Discussion@python.org
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