On Mon, Jul 5, 2021 at 11:19 AM Stefan van der Walt <stef...@berkeley.edu> wrote:
> The reason why Gagandeep started working on this is so we can have the > never-copy behavior in the `numpy.array_api` namespace. For the `asarray` > function there, the `copy` keyword is still boolean, with description: > > Whether or not to make a copy of the input. If True, always copies. > If False, never copies for input which supports DLPack or the buffer > protocol, > and raises ValueError in case that would be necessary. > If None , reuses existing memory buffer if possible, copies > otherwise. > Default: None. > > In the end I think that's better than strings, and way better than enums - > we just can't have that in the main namespace, because we can't change what > `False` does. > > > I agree <https://github.com/numpy/numpy/pull/19173#issuecomment-858226896> > that this is a good API (although not everybody else does). > <https://github.com/numpy/numpy/pull/19173#issuecomment-860314626> > > W.r.t. NumPy's API: it could be okay to change the behavior of copy=False > to make it more strict (no copies ever), because then at least errors will > be raised and we can provide a message with instructions on how to fix it. > Resurfacing this discussion, since Sebastian asked me to comment. After some reflection, I think my favorite solution now is True/False/None, including a deprecation cycle to migrate existing users of copy=False to use copy=None. This is the simplest adaptation of the existing argument, and in many cases where users are writing copy=False they may actually not be intending the current "maybe copy" behavior. Strings would be appropriate if we were starting from scratch, but breaking backwards compatibility is very problematic. I do like enums, but I recognize that they are not currently used in NumPy/SciPy, so they feel a little out of place, and expanding NumPy's namespace to add more enums also has a cost. I don't think the meme I linked to is entirely appropriate, because these aren't just three arbitrary modes -- two of the cases here really are "yes" or "no" copy, and the other is "maybe", which is a pretty common meaning for "None" as a default value (and users will rarely be writing copy=None themselves).
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