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Multiprocessing returns Array, RawArray of wrong length python 3.10.4 #98447
Description
Bug report
When initializing Array or RawArray of type int, wrong length of the arrays is returned
Reproducible example:
from multiprocessing import RawArray, RawValue, Array, Value
a = Array('d',12)
X = np.frombuffer(a.get_obj())
print(X) # [0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
a = Array('i',12)
X = np.frombuffer(a.get_obj())
print(X) # [0. 0. 0. 0. 0. 0.]
a = RawArray('d',12)
X = np.frombuffer(a)
print(X) # [0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
a = RawArray('i',12)
X = np.frombuffer(a)
print(X) # [0. 0. 0. 0. 0. 0.]
Your environment
working with vscode
conda-forge python 3.10.4
using ubuntu uname-a: 5.11.0-46-generic #51~20.04.1-Ubuntu SMP Fri Jan 7 06:51:40 UTC 2022
- CPython versions tested on: conda-forge python 3.10.4
- Operating system and architecture: using ubuntu uname-a: 5.11.0-46-generic 51~20.04.1-Ubuntu
Activity
mdboom commentedon Oct 19, 2022
The buffer interface doesn't retain type information about the items in the array, so using
np.frombufferdefaults todouble(8 bytes per item), even when the type in the array isi(4 bytes per item) since converting to a buffer throws that information out.I think you want to use
np.asarray(a)instead to get the behaviour you want -- it will correctly look at the type of the array (using the memoryview API), and it likewise avoids the memory copy.tendermonster commentedon Oct 20, 2022
Thanks for quick response