Load pickle file(comes from python3) in python2

Question

I have a pickle file, with

>>> with open("wikilinks.pickle", "rb") as f:
...     titles, links = pickle.load(f)
... 
>>> len(titles)
13421

I can load it in python3. However, when I try to load it in python2, I get this message: Traceback (most recent call last):

  File "<stdin>", line 2, in <module>
  File "/usr/lib/python2.7/pickle.py", line 1378, in load
    return Unpickler(file).load()
  File "/usr/lib/python2.7/pickle.py", line 858, in load
    dispatch[key](self)
  File "/usr/lib/python2.7/pickle.py", line 886, in load_proto
    raise ValueError, "unsupported pickle protocol: %d" % proto
ValueError: unsupported pickle protocol: 3

So how to load it in python2?

Liang Xiao · Accepted Answer · 2017-04-08 06:05:58Z

37

Read in python3 and save it as python2 format

#!/usr/bin/env python3

import pickle

with open("a.pkl", "rb") as f:
    w = pickle.load(f)

pickle.dump(w, open("a_py2.pkl","wb"), protocol=2)

Then you can load a_py2.pkl in python2.

answered Apr 8, 2017 at 6:05

Liang Xiao

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user4815162342 · Accepted Answer · 2015-04-12 07:55:33Z

15

The default pickling protocol used by default in Python 3 is incompatible with the protocol used by Python 2. However, if you can modify the code that produces wikilink.pickle, you can tell it to use one of the earlier protocols (0, 1, or 2) which Python 2 will understand just fine.

Be warned, though, that Python 3 strings will come up as Unicode strings in Python 2, which may be surprising in some use cases.

$ python3
Python 3.4.1 (default, May 19 2014, 17:23:49) 
[GCC 4.9.0 20140507 (prerelease)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> pickle.dumps([1, 2, 'abc'], 2)
b'\x80\x02]q\x00(K\x01K\x02X\x03\x00\x00\x00abcq\x01e.'
>>> 
$ python 
Python 2.7.8 (default, Jul  1 2014, 17:30:21) 
[GCC 4.9.0 20140604 (prerelease)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cPickle
>>> cPickle.loads('\x80\x02]q\x00(K\x01K\x02X\x03\x00\x00\x00abcq\x01e.')
[1, 2, u'abc']

answered Apr 12, 2015 at 7:55

user4815162342

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3 Comments

Chao Zhang Over a year ago

so how to slove the unicode problem?

user4815162342 Over a year ago

@ChaoZhang Convert the Unicode strings to utf8, or update the code to deal with them.

Chao Zhang Over a year ago

i call python2 to convert unicode and long integer after python3 process, thus the output pickle file can use in python2 system directly, lol

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