#!/usr/bin/env python3

"""
Foo is a subclass of str, and uses __new__.

Goo is a nearly identical class, but uses __init__.

When the Foo constructor is called via a multiprocessing Pool, the call stack somehow gets garbled, and the output gets sent right back into the constructor:

Called Foo.__new__ with args = (u'TIMESTAMP', u'INPUT0')
Called Foo.__new__ with args = ('TIMESTAMP OUTPUT0',)

When Foo is swapped out for Goo, the expected result is obtained:

Called Goo.__init__ with args = (u'TIMESTAMP', u'INPUT0')
<Goo TIMESTAMP OUTPUT0>

The problem also goes away when a multiprocessing.pool.ThreadPool is used instead of a (process) Pool:

Called Foo.__new__ with args = (u'TIMESTAMP', u'INPUT0')
TIMESTAMP OUTPUT0

Seen in Python 2.7.9 and 3.4.5
"""

from __future__ import print_function, unicode_literals

import multiprocessing.pool as mpp
import multiprocessing as mp

# ######################################################################

def main():
    # pool = mpp.ThreadPool(1)
    pool = mp.Pool(1)
    getter = pool.apply_async( Foo, ('TIMESTAMP', 'INPUT0'), {} )
    print( getter.get(timeout=3) )
    pool.close()
    return

# ######################################################################

class Foo(str):
    def __new__(cls, *args):
        print( 'Called Foo.__new__ with args = ' + repr(args) )
        if len(args) != 2:
            raise ValueError( 'Bad Foo input: ' + repr(args) )
        tmp = args[0] + ' ' + args[1].replace('INPUT', 'OUTPUT')
        return str.__new__(cls, tmp)

# ######################################################################

class Goo(object):
    def __init__(self, *args):
        print( 'Called Goo.__init__ with args = ' + repr(args) )
        if len(args) != 2:
            raise ValueError( 'Bad Goo input: ' + repr(args) )
        self.name = args[0] + ' ' + args[1].replace('INPUT', 'OUTPUT')
        return
    def __repr__(self):
        return '<Goo ' + repr(self.name) + '>'

# ######################################################################

if __name__ == '__main__':
    main()