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

Question

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 1

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.

Answer 2

Pickle uses different protocols to convert your data to a binary stream.

• In python 2 there are 3 different protocols (0, 1, 2) and the default is 0.

• In python 3 there are 5 different protocols (0, 1, 2, 3, 4) and the default is 3.

You must specify in python 3 a protocol lower than 3 in order to be able to load the data in python 2. You can specify the protocol parameter when invoking pickle.dump.