classification
Title: Unpickling objects with recursive references and partials fail due to incomplete state passed to __setstate__
Type: behavior Stage:
Components: Interpreter Core Versions: Python 3.6, Python 3.4, Python 3.5
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: aleneum
Priority: normal Keywords:

Created on 2018-04-09 12:37 by aleneum, last changed 2018-04-09 15:31 by aleneum.

Messages (2)
msg315127 - (view) Author: Alexander Neumann (aleneum) Date: 2018-04-09 12:37
The code below causes a 

   AttributeError: 'Event' object has no attribute 'name'

It seems like the entries of `Machine.events` are not available during `__setstate__`. However, the behaviour depends on the Python version.

For Python 3.6.4 it's always the 'first' (as in it's always 'to_A' which has been added first) element in `Machine.events` that is incomplete. For Python 3.4.8 and 3.5.5 it looks like a racing condition since sometimes there is no error, sometimes its the first or the second element which is incomplete.
Letting `Machine` serve as its own model and pickling that does work for all three versions.

Tested on MacOS High Sierra.

```
import pickle
from functools import partial


class Event:

    def __init__(self, name, machine):
        self.name = name
        self.machine = machine

    def trigger(self):
        pass


class Machine:

    def __init__(self, model, states):
        self.events = {}
        self.model = model if model != 'self' else self

        for state in states:
            trigger = 'to_%s' % state
            self.events[trigger] = Event(trigger, self)
            trig_func = partial(self.events[trigger].trigger)
            setattr(self.model, trigger, trig_func)

    def __getstate__(self):
        return self.__dict__

    def __setstate__(self, state):
        self.__dict__.update(state)
        print(self.events['to_B'].name)
        print(self.events['to_A'].name)


class Model:

    def __init__(self):
        self.machine = Machine(self, states=['A', 'B'])

model = Model()
dump = pickle.dumps(model)
model2 = pickle.loads(dump)
```
msg315130 - (view) Author: Alexander Neumann (aleneum) Date: 2018-04-09 15:31
Changed issue title to summarise the actual problem better.
History
Date User Action Args
2018-04-09 15:31:56aleneumsetmessages: + msg315130
title: Pickling objects with recursive references and partials fail -> Unpickling objects with recursive references and partials fail due to incomplete state passed to __setstate__
2018-04-09 12:37:25aleneumcreate