Unpickle already pickled file

Question

I have already pickled file and i use to un-pickle it

with open(meta_path, 'rb') as f:
    result = pickle.load(f)

on my machine python3 version is 3.6.9 python2 version is 2.7.17

most of answers suppose to use protocol=2 during dumping as this answer but the problem is the file is already dumped I did not pickled it, that is why I do not know which protocol was used. Can anyone help me to un-pickle this file?

Answer 1

You can use pickletools to identify the Protocol version. Have a look in the stdout which version was used. Probably Python2 is not able to unpickle dumps using protocol versions > 2.

import pickle
import pickletools

obj = {'load': pickle.load}

# dump all Python3 supported versions
for x in range(0, 6):
    filename = '/tmp/data_v{x}.pickle'
    with open(filename, 'wb') as f:
        pickle.dump(obj, f, protocol=x)

    with open(filename, 'rb') as f:
        print(pickletools.dis(f))

Out for Python3 (truncated):

highest protocol among opcodes = 0
    0: }    EMPTY_DICT
    1: q    BINPUT     0
    3: X    BINUNICODE 'load'
   12: q    BINPUT     1
   14: c    GLOBAL     'pickle load'
   27: q    BINPUT     2
   29: s    SETITEM
   30: .    STOP
highest protocol among opcodes = 1
    0: \x80 PROTO      2
    2: }    EMPTY_DICT
    3: q    BINPUT     0
    5: X    BINUNICODE 'load'
   14: q    BINPUT     1
   16: c    GLOBAL     'pickle load'
   29: q    BINPUT     2
   31: s    SETITEM
   32: .    STOP
highest protocol among opcodes = 2
    0: \x80 PROTO      3
    ...