For converting Python 2 pickles to Python 3

kimchi.py

# kimchi.py
# For converting Python 2 pickles to Python 3

import os
import dill
import pickle
import argparse


def convert(old_pkl):
    """
    Convert a Python 2 pickle to Python 3
    """
    # Make a name for the new pickle
    new_pkl = os.path.splitext(os.path.basename(old_pkl))[0]+"_p3.pkl"

    # Convert Python 2 "ObjectType" to Python 3 object
    dill._dill._reverse_typemap["ObjectType"] = object

    # Open the pickle using latin1 encoding
    with open(old_pkl, "rb") as f:
        loaded = pickle.load(f, encoding="latin1")

    # Re-save as Python 3 pickle
    with open(new_pkl, "wb") as outfile:
        pickle.dump(loaded, outfile)


if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        description="Convert a Python 2 pickle to Python 3"
    )

    parser.add_argument("infile", help="Python 2 pickle filename")

    args = parser.parse_args()

    convert(args.infile)

Hiya - this is meant for unpickling scikit-learn Estimators. For pandas you could try out this suggestion

Thanks! This is great, worked for me. But there's one thing I don't understand. The script sets
dill._dill._reverse_typemap["ObjectType"] = object

But it doesn't use dill, it uses pickle.load and pickle.dump. So how does dill do anything here?

Hi @nbecker; this gist is associated with a longer blog post, which may answer your question!

In my case I have to convert a joblib jl saved file, how to adapt the script for joblib?
I have tried to map b'ObjectType' but it seems it is not enough:

import os
import joblib
import dill

dill._dill._reverse_typemap["ObjectType"] = object

DATA_PATH = '/root'

tfidf_vectorizer, _ = joblib.load(os.path.join(DATA_PATH,'nmf_topic_model/tfidf_mpd.jl'))
nmf_model, _ = joblib.load(os.path.join(DATA_PATH,'nmf_topic_model/nmf_mpd.jl'))

I have tried to tap the joblib file .../joblib/numpy_pickle.py so that the class NumpyUnpickler has a ovverride load method like

    def load(self):
        eggs = pickle.load(self.file_handle, encoding='latin1')
        return eggs

and I have put

import dill
dill._dill._reverse_typemap["ObjectType"] = object

Another attempt was to add the encoding directly in the NumpyUnpickler init:

def __init__(self, filename, file_handle, mmap_mode=None):
     Unpickler.__init__(self, self.file_handle, encoding="latin1")