8000 Improve the error message for invalid typecodes in `multiprocessing.{Array,Value}` · Issue #133017 · python/cpython · GitHub
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Improve the error message for invalid typecodes in multiprocessing.{Array,Value} #133017

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tomasr8 opened this issue Apr 26, 2025 · 0 comments
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Improve the error message for invalid typecodes in multiprocessing.{Array,Value} #133017

tomasr8 opened this issue Apr 26, 2025 · 0 comments
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stdlib Python modules in the Lib dir topic-multiprocessing type-feature A feature request or enhancement

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tomasr8 commented Apr 26, 2025 •
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Feature or enhancement

Proposal:

More discussion: #132504 (comment)

This is the current message which is not very clear (it comes from ctypes.sizeof):

>>> from multiprocessing import Array
>>> Array('x', 1)
...
TypeError: this type has no size

I propose we change it to:

>>> from multiprocessing import Array
>>> Array('x', 1)
TypeError: bad typecode (must be a ctypes type or one of c, b, B, u, h, H, i, I, l, L, q, Q, f or d)

This is modeled after the error message in array.array which is more informative:

>>> array('x')
...
ValueError: bad typecode (must be b, B, u, w, h, H, i, I, l, L, q, Q, f or d)

(A ValueError seems like a more appropriate option for multiprocessing as well, but that'd be a breaking change)
Note that, multiprocessing.Array (and Value) does not support the 'w' typecode while array.array does.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

#132504 (comment)

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