ValueError: unsupported pickle protocol: 3, python2 pickle can not load the file dumped by python 3 pickle?

python python-3.x python-2.7 pickle valueerror
Aleeee picture Aleeee · Sep 15, 2014 · Viewed 122.4k times · Source

I use pickle to dump a file on python 3, and I use pickle to load the file on python 2, the ValueError appears.

So, python 2 pickle can not load the file dumped by python 3 pickle?

If I want it? How to do?

Answer

Matthias picture Matthias · Sep 15, 2014

You should write the pickled data with a lower protocol number in Python 3. Python 3 introduced a new protocol with the number 3 (and uses it as default), so switch back to a value of 2 which can be read by Python 2.

Check the protocolparameter in pickle.dump. Your resulting code will look like this.

pickle.dump(your_object, your_file, protocol=2)

There is no protocolparameter in pickle.load because pickle can determine the protocol from the file.

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