[issue29108] Python 3.6.0 multiprocessing map_async callback

[Jose Miguel Colella]

Jose Miguel Colella added the comment:

Hello David,
Thanks for your response. Improvements to the documentation could clear this 
misunderstanding. I had initially believed that after transforming with the 
function passed to the map, it would use the callback on each of the result 
arguments. 
Just to understand the use case of the callback. So basically it should not 
return anything and be a simple print?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29108] Python 3.6.0 multiprocessing map_async callback

[Davin Potts]

Davin Potts added the comment:

This appears to be working as designed.  The purpose of the callback is to 
receive a single argument (nominally, the ready result from the map operation) 
and perform its task (whatever it may be) very quickly so as not to further 
delay the handing back of results from the map operation.

Attempting to read into your comments, it sounds like you were perhaps 
expecting the return from the callback to appear somewhere?  If that was your 
expectation then no, that is not the purpose of a callback here.  Any 
transformation of input data to the final output data is performed by the 
function being applied by the map.  While there are many potential uses for a 
callback, its stated requirement is that it be as quick an operation as 
possible as opposed to something that further transforms the results or 
anything like a "reduce" operation which is not necessarily quick.

If you think this needs clarification in the documentation, please suggest 
something?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29108] Python 3.6.0 multiprocessing map_async callback

[Ned Deily]

Changes by Ned Deily :


--
nosy: +davin

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29108] Python 3.6.0 multiprocessing map_async callback

[Jose Miguel Colella]

Jose Miguel Colella added the comment:

The result is:
Here: [1, 4, 9]
[1, 4, 9]

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29108] Python 3.6.0 multiprocessing map_async callback

[Jose Miguel Colella]

New submission from Jose Miguel Colella:

Hello I am trying to use the callback for the map_async method for Pool, but 
have found a bug. In the below code, only the print statement is carried out, 
the return is completely ignored. Is this working as designed or is this a bug?

from multiprocessing import Pool


def f(x):
return x * x


def s(x):
print(f'Here: {x}')
return type(x)


if __name__ == '__main__':
with Pool(5) as p:
result = p.map_async(f, [1, 2, 3], callback=s)
q = result.get()
print(q)

--
components: Library (Lib)
files: main2.py
messages: 284295
nosy: Jose Miguel Colella
priority: normal
severity: normal
status: open
title: Python 3.6.0 multiprocessing map_async callback
type: behavior
versions: Python 3.6
Added file: http://bugs.python.org/file46084/main2.py

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com