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?
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5If you are stuck with already-written pickled files, then check out: stackoverflow.com/questions/34571063/…– rysquiCommented Jan 3, 2016 at 1:58
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2 Answers
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.
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 is0.In python 3 there are 5 different protocols (
0,1,2,3,4) and the default is3.
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.
answered Sep 15, 2014 at 8:32
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14Just for future reference, apparently there's a protocol
5that was introduced in Python 3.8 as well which is not compatible with earlier versions. Commented Mar 20, 2020 at 18:12 -