How can I find out / print with which version of the protocol a pickle file has been generated

Question

In some cases, when I load an existing pickle file, and after that dump it again, the size is almost halved.

I wonder why, and the first suspect is the protocol version.
Can I somehow find out with which protocol version a file was pickled?

Asked By: Jacques de Hooge

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Source

Answer 1

There may be a more elegant way but to get down to the metal you can use pickletools:

import pickle
import pickletools
s = pickle.dumps('Test')
proto_op = next(pickletools.genops(s))
assert proto_op[0].name == 'PROTO'
proto_ver = proto_op[1]

To figure out the version required to decode this, you’ll need to maximum protocol version of each opcode:

proto_ver = max(op[0].proto for op in pickletools.genops(s))

Answered By: user2722968

Answer 2

A convenient solution in command line by using pickletools:

$ python -m pickletools filename.pickle
    0: x80 PROTO      5
    2: x95 FRAME      14451
   11: ]    EMPTY_LIST
   12: x94 MEMOIZE    (as 0)
   ...
14459: b    BUILD
14460: a    APPEND
14461: .    STOP
highest protocol among opcodes = 5

The first line with PROTO showing the pickle Protocol version of the file. And the last line also give you infomation abouth the protocol.

Answered By: YaOzI

How can I find out / print with which version of the protocol a pickle file has been generated

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