Unsupported Pickle Protocol: 5 Error Solved

The “Unsupported Pickle Protocol: 5” error typically occurs when we are trying to load a pickled object using a protocol version not supported by the current Python environment. The pickle module in Python is used for serializing and deserializing Python objects, allowing them to store them in a file or transfer them between processes.

When is the Unsupported Pickle Protocol: 5 Error Encountered?

Protocol 5, in particular, was introduced in Python 3.8. We will encounter this error if we use an older version of Python that does not support protocol 5.

These are the following ways for the error to occur:

1. Cross-version compatibility: If working with a codebase that involves pickling and unpickling objects across different Python versions, one may encounter the “Unsupported Pickle Protocol: 5″ error when trying to unpickle objects serialized with protocol 5 in an older Python version.

This situation can arise when sharing pickled objects between different systems or migrating code to a new Python version.

2. Python version upgrade: When upgrading the Python version to a newer release that supports protocol 5, the user may encounter this error when attempting to load pickled objects created with the newer protocol.

In this case, we may need to update our code or the pickled objects to use a compatible protocol version supported by both the old and new Python versions.

3. Library compatibility: If using a third-party library or framework that utilizes pickling and the library was updated to use protocol 5, but Python environment does not support it, we may encounter the “Unsupported Pickle Protocol: 5″ error.

This can occur if we update the library or framework to a version that uses the latest pickle protocol while still using an older version of Python.

4. Distributed systems: In distributed computing environments where different nodes or processes communicate by pickling and unpickling objects, we may encounter this error if there is a mismatch between the Python versions used on different nodes.

If one node serializes objects with protocol 5 and another node attempts to unpickle them with an older Python version, the error will occur.


Here is an example to show the Unsupported Pickle Protocol: 5 error. In this example, we first pickle the numbers list using protocol 5 by specifying protocol=5 in pickle.dump().

The pickled object is stored in a file named ‘numbers.pickle’. Then, when we try to unpickle the object using pickle.load(), we encounter the “Unsupported Pickle Protocol: 5″ error if our Python version does not support protocol 5.


import pickle

# Example object
numbers = [1, 2, 3, 4, 5]

# Pickling the object with protocol 5
with open('numbers.pickle', 'wb') as file:
    pickle.dump(numbers, file, protocol=5)

# Attempting to unpickle with unsupported protocol
    with open('numbers.pickle', 'rb') as file:
        unpickled_numbers = pickle.load(file)
except Exception as e:
    print(f"Error: {str(e)}")

How can the Unsupported Pickle Protocol: 5 Issue Be Resolved?

The below ways needs to be followed to resolve the error:

To upgrade Python: If we are using an older version of Python, consider upgrading to a version that supports protocol 5 (e.g., Python 3.8 or later).

To specify a compatible protocol version: If we have control over the code that generates the pickled object, we can explicitly specify a compatible protocol version when using the pickle.dump() function. For example, we can use pickle.dump(obj, file, protocol=4) to use protocol version 4, which is supported in Python 3.4 and later.

To downgrade the protocol version: If we use a pickled object generated by a newer version of Python, we can try downgrading the protocol version when loading the object. Instead of using the default pickle.load() function, we can use pickle.load(file, fix_imports=True, encoding='latin1') to load the object using the highest protocol version supported by our Python version.


What is pickled object?

A pickled object is a Python object that has been serialized using the pickle module. Pickling converts a Python object hierarchy into a byte stream, which can be saved to a file or transferred across a network.

The pickled object can later be unpickled or deserialized to recreate the original Python object. The pickle module allows you to work with various Python objects, including built-in data types (such as integers, strings, lists, dictionaries), custom objects, functions, and more.

It supports the serialization and deserialization of complex object hierarchies, preserving their internal structure and state.

What measures should be taken while resolving the error?

It’s important to note that while pickle is a convenient way to serialize and deserialize Python objects, caution should be exercised when unpickling data from untrusted or unreliable sources. Unpickling maliciously crafted or tampered pickled objects can lead to security vulnerabilities.


In summary, the Unsupported Pickle Protocol: 5 error indicates a mismatch between the pickle protocol version used for serialization and the protocol version supported by your current Python environment.

Resolving the error typically involves upgrading Python to a version that supports protocol 5, specifying a compatible protocol version explicitly when pickling, or downgrading the protocol version when unpickling.


  1. Pickle Module

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