Description

tendermonster

opened on Oct 19, 2022

Issue body actions

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

1. tendermonster

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Oct 19, 2022
2. AlexWaygood

   added

   topic-multiprocessing

   on Oct 19, 2022
3. AlexWaygood

   added this to Multiprocessing issueson Oct 19, 2022
4. mdboom commented on Oct 19, 2022

   

   mdboom

   on Oct 19, 2022

   Contributor

   More actions

   The buffer interface doesn't retain type information about the items in the array, so using np.frombuffer defaults to double (8 bytes per item), even when the type in the array is i (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.
5. mdboom

   closed this as completedon Oct 19, 2022
6. mdboom

   moved this to Done in Multiprocessing issueson Oct 19, 2022
7. tendermonster commented on Oct 20, 2022

   

   tendermonster

   on Oct 20, 2022

   Author

   More actions

   Thanks for quick response

Issue actions