[issue46593] memoryview lacks support for half floats

[Antoine Pitrou]

New submission from Antoine Pitrou <pitrou at free.fr>:

The struct module has support for half-floats (the "e" format code) but support is not fully enabled in the memoryview object.

Let's contrast float32 (the "f" format code), which you can cast to, and read as Python objects:

>>> a = np.array([0.0, -1.5], np.float32())
>>> list(memoryview(a))
[0.0, -1.5]
>>> memoryview(a.tobytes()).cast('f').tolist()
[0.0, -1.5]

and float16, where support is minimal (casting forbidden, reading as Python objects unimplemented):

>>> a = np.array([0.0, -1.5], np.float16())
>>> list(memoryview(a))
Traceback (most recent call last):
  File "<ipython-input-15-102982f8ac8e>", line 1, in <module>
    list(memoryview(a))
NotImplementedError: memoryview: format e not supported

>>> memoryview(a.tobytes()).cast('e').tolist()
Traceback (most recent call last):
  File "<ipython-input-25-78df215a7360>", line 1, in <module>
    memoryview(a.tobytes()).cast('e').tolist()
ValueError: memoryview: destination format must be a native single character format prefixed with an optional '@'

----------
components: Interpreter Core
messages: 412205
nosy: mark.dickinson, meador.inge, pitrou
priority: normal
severity: normal
stage: needs patch
status: open
title: memoryview lacks support for half floats
type: enhancement
versions: Python 3.11

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue46593>
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