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Masked is unhashable

See original GitHub issue

Description

Masked classes are unhashable.

Expected behavior

It is washable, like the unmasked version.

Actual behavior

hash(X) returns a TypeError because it is unhashable.

Steps to Reproduce

from astropy import units as u
from astropy.utils.masked import Masked
MQ = Masked(u.Quantity)
hash(MQ(2 * u.km))  # raises TypeError

System Details

macOS-10.16-x86_64-i386-64bit Python 3.8.2 | packaged by conda-forge | (default, Apr 24 2020, 07:56:27) [Clang 9.0.1 ] Numpy 1.18.4 astropy 4.3.dev1486+gddc6fb76f.d20210505 Scipy 1.4.1 Matplotlib 3.4.1

Issue Analytics

State:
Created 2 years ago
Comments:5 (5 by maintainers)

Top GitHub Comments

1reaction

mhvkcommented, May 6, 2021

@nstarman - only Quantity scalars are hashable, which is to have an analogy with the np.float64 scalars, etc. (even though the analogy is not perfect, since with a scalar length quantity q += 1*u.cm changes the object in-place, while the equivalent for a numpy scalar creates a new object). For the masked class, having a hashable object makes even less sense, I think, since the mask itself is very explicitly meant to be mutable.

0reactions

mhvkcommented, May 6, 2021

I checked and neither np.ma.masked, nor a scalar np.ma.MaskedArray are hashable. Since the problem that triggered this issue is unrelated, I’ll close this for now.

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