[New-bugs-announce] [issue32538] Multiprocessing Manager on 3D list - no change of the list possible

Johannes report at bugs.python.org
Fri Jan 12 10:05:56 EST 2018

New submission from Johannes <johannes.jaegers at gmx.de>:

I have the following code, which works without multiprocessing:

data[0][0][0] = 5
data[0][0][1] = "5" # data in the array is mixed with float and str

#=> [[[5, '5', '', '', '', '', '', '', '', '', '', '']]]

Now I want to use Multiprocessing and every process should be able to change the 3D list. This doesn't work and no error message is shown.

from multiprocessing import Process, Manager
data[0][0][0] = 5
data[0][0][1] = "5"

#=> [[['', '', '', '', '', '', '', '', '', '', '', '']]]

I found the following text:

Create a shared list object and return a proxy for it.
Changed in version 3.6: Shared objects are capable of being nested. For     
example, a shared container object such as a shared list can contain 
other shared objects which will all be managed and synchronized by the 

Unfortunately it also doesn't work with 3.6.3, same problem as before! But as it should work, I guess it's a bug?

I use Ubuntu 16.04...

components: Interpreter Core
messages: 309858
nosy: John_81
priority: normal
severity: normal
status: open
title: Multiprocessing Manager on 3D list - no change of the list possible
type: behavior
versions: Python 3.6

Python tracker <report at bugs.python.org>

More information about the New-bugs-announce mailing list