python 2.7,unsupported pickle protocol: 3

This error occurs when trying to load a pickle file that was created with a higher protocol version than the one supported by the current version of Python.

Python 2.7 supports protocol versions 0, 1, 2, and 3, while Python 3.x supports protocol versions 0, 1, 2, 3, 4, and 5.

To resolve the issue, you can either upgrade to a higher version of Python that supports the pickle protocol used to create the pickle file, or regenerate the pickle file using a protocol version that is compatible with Python 2.7.

For example, to generate a pickle file with protocol version 2, you can use the following code:

import pickle

with open('data.pkl', 'wb') as f:
    pickle.dump(data, f, protocol=2)

Then, when loading the pickle file in Python 2.7, use the following code:

import pickle

with open('data.pkl', 'rb') as f:
    data = pickle.load(f)