Cloudpickle non-deterministic dump when file is innocuously modified

[richardwu]

Cloudpickle seems to produce non-deterministic dumps when the file's formatting is "innocuously" modified (e.g., formatting changes outside of pickled object's definition) whereas dill and pickle would produce deterministic dumps.

For example, inserting a blank line anywhere after where the pickled function foo is defined will initially produce a different hash, then subsequently produce the same hash upon successive runs:

import cloudpickle
import dill
import pickle

def foo():
    pass

def get_cpickle():
    return cloudpickle.dumps(foo)

def get_dill():
    return dill.dumps(foo)

def get_pickle():
    return pickle.dumps(foo)

if __name__ == '__main__':
    print('Cpickle:', hash(get_cpickle()))
    print('Dill:', hash(get_dill()))
    print('Pickle:', hash(get_pickle()))

Command:

PYTHONHASHSEED=1 python bad_pickle.py

First run:

Cpickle: -185195056977094428
Dill: 1827482599472099751
Pickle: -2221802750934099445

Second run:

Cpickle: 5072829361071368526
Dill: 1827482599472099751
Pickle: -2221802750934099445

Blank line inserted after print('Cpickle:', ...) (third run):

Cpickle: -185195056977094428
Dill: 1827482599472099751
Pickle: -2221802750934099445

Fourth run:

Cpickle: 5072829361071368526
Dill: 1827482599472099751
Pickle: -2221802750934099445

This was tested on the following versions:

Cpickle version: 1.2.2
Dill version: 0.2.7.1
Python version: 3.6.10 (default, Jan  1 2020, 00:00:00)

This seems like perhaps Cloudpickle is also hashing some eventually cached version of the source file (e.g., .pyc).

This is also somewhat related to #120 .

[pierreglaser]

Thanks for your report. What you're reporting seems plausible, but I cannot reproduce on my machine (Ubuntu 18, Python 3.6, same cloudpickle version)...

[ogrisel]

For me, inserting a blank line changes the hash both for cloudpickle and dill. But the hash stays consistent across runs without code change.

[ogrisel]

Anyway, having deterministic pickles is probably out of scope for cloudpickle so I would be in favor of closing this issue.