multiprocessing failing when function contains a class on the same file

Problem Description

The following code executes properly from the command line but not within spyder. The program hangs and the command window show the traceback pasted below. Placing the class code (everything before if __name__ == "__main__") in a separate file and importing the class solves the problem - but it is not clear why this code does not work as it does when executing from the command line.

What steps reproduce the problem?

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
from multiprocessing import Pool
class myClass():
    
    def __init__(self,q_seed=0,*args,**kwargs,) :
        self.q_seed = q_seed
        print(self.q_seed)

def simulateLocPool(kwargs) : 

    m = myClass(**kwargs)  
    return m   

#%%
if __name__ == "__main__":
    
    nboots = 10
    nprocs = 10
    
    # construct list to pass to processes
    iterlist = []
    kwargs = {'q_seed' : 0}
    
    # change seeds
    for bootn in range(nboots):
        newkw = kwargs.copy()
        newkw['q_seed'] = kwargs['q_seed'] + bootn
        iterlist.append((newkw)) 
    
    #spawn nboots processes, nprocs at once    
    pool = Pool(processes=nprocs)
    allmodels = pool.map(simulateLocPool,(iterlist))
    pool.close()
    pool.join()

Output

The code hangs with the following traceback

Exception in thread Thread-23:
Traceback (most recent call last):
  File "/Users/moroa/opt/miniconda3/lib/python3.9/threading.py", line 954, in _bootstrap_inner
    self.run()
  File "/Users/moroa/opt/miniconda3/lib/python3.9/threading.py", line 892, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/moroa/opt/miniconda3/lib/python3.9/multiprocessing/pool.py", line 576, in _handle_results
    task = get()
  File "/Users/moroa/opt/miniconda3/lib/python3.9/multiprocessing/connection.py", line 256, in recv
    return _ForkingPickler.loads(buf.getbuffer())
AttributeError: Can't get attribute 'myClass' on <module 'spyder_kernels.console.__main__' from '/Users/moroa/opt/miniconda3/lib/python3.9/site-packages/spyder_kernels/console/__main__.py'>

Expected output

A printout of digits from 0 to 9

Versions

• Spyder 5.1.5|Python 3.9.5 64-bit | Qt 5.12.10 | PyQt5 5.12.3 | Darwin 20.6.0
• Operating System name/version: MacOS 11.5.2

[ccordoba12]

I don’t know why this is not working, but

• If you’re running your code in an unsaved file (as @athompson673 seems to be doing), it could be related to this because multiprocessing could have problems pickling code in that situation.
• The work @impact27 is doing in PR #14025 could help at least to debug these problems.

[ccordoba12]

Thanks @impact27 for your help with this!

This will be fixed in our next version (5.2.2), to be released next week.