Hi all, I would like to share the first formal draft of
NEP 50: Promotion rules for Python scalars
with everyone. The full text can be found here:
https://numpy.org/neps/nep-0050-scalar-promotion.html
NEP 50 is an attempt to remove value-based casting/promotion. We wish
to replace it with clearer rules for the resulting dtype when mixing
NumPy arrays and Python scalars. As a brief example, the proposal
allows the following (unchanged):
>>> np.array([1, 2, 3], dtype=np.int8) + 100
np.array([101, 102, 103], dtype=np.int8)
While clearing up confusion caused by the value-inspecting behavior
that we see sometimes, such as:
>>> np.array([1, 2, 3], dtype=np.int8) + 300
np.array([301, 302, 303], dtype=np.int16) # note the int16
Where 300 is too large to fit an ``int8``. As well as removing the
special behavior of 0-D arrays or NumPy scalars:
>>> res = np.array(1, dtype=np.int8) + 100
>>> res.dtype
dtype('int64')
This is the continuation of a long discussion (see the "Discussion"
section), including the poll I once posted:
https://discuss.scientific-python.org/t/poll-future-numpy-behavior-when-mixing-arrays-numpy-scalars-and-python-scalars/202
I would be happy for any feadback, be it just editorial or fundamental
discussion. There are many alternatives which I have tried to capture
in the NEP.
So lets discuss here, or on discuss:
https://discuss.scientific-python.org/t/nep-50-promotion-rules-for-python-scalars/280
For smaller edits, don't hesitate to open a NumPy PR, or propose edits
on my branch (you can use the edit button to create a PR):
https://github.com/seberg/numpy/blob/nep50/doc/neps/nep-0050-scalar-promotion.rst
An important part of moving forward will be assessing the real world
impact. To start that process, I have created a branch as a draft PR
(at this time):
https://github.com/numpy/numpy/pull/21626
It is missing some parts, but should allow preliminary testing. The
main missing part is that the integer warnings and errors are less
strict than proposed in the NEP.
It would be invaluable to get a better idea to what extent existing
code, especially end-user code, is affected by the proposed changes.
Thanks in advance for any input! This is a big, complicated proposal,
but finding a way forward will hopefully clear up a source of confusion
and inconsistencies that make both maintainers and users life harder.
Cheers,
Sebastian
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