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What causes the error “pickle.UnpicklingError: invalid load key”?

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What causes the error "pickle.UnpicklingError: invalid load key"?
forever_romantico_94
forever_romantico_94 Begginer

I am an aspiring data scientist who has been working on a project for the past three weeks. My code involves using the pickle library to save and load large datasets. Recently, I updated the version of Python I am using from 3.7 to 3.8. Since then, I have been experiencing an error message with the pickle.load() function. The error message I get is, “pickle.UnpicklingError: invalid load key, ‘x’.”

I have tried to read the pickle documentation to understand what the error message means, but I cannot find any reference to it. I have checked my code to see if there are any spelling mistakes or invalid characters, but I cannot seem to find any. I have also tried to recreate the pickle file using the new version of Python, hoping it would work, but still no luck.

I am not sure what could be causing this error, and I need help in identifying the root cause. Below is an excerpt of my code that generates the error.


with open('dataset.pkl', 'rb') as f:
try:
dataset = pickle.load(f)
except pickle.UnpicklingError as e
print(e)

Can anyone help me understand what could be causing this error and how I can fix it?

debuggingerror handlingpicklepythonserialization
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    illanes.leonardo Begginer
    2017-11-15T12:18:32+00:00Added an answer about 5 years ago

    Hey there, it seems like you are facing issues with the “pickle.UnpicklingError: invalid load key” error in your Python code. This issue can be caused by a number of factors, including incompatible versions of Python, serialization issues, or file corruption.

    First of all, make sure that you are using the latest version of Python. If you are using an older version, then this may be the root cause of the problem. This error has been reported in versions prior to Python 2.3.5 and Python 2.4.2. So, if you are using an older version, consider upgrading to the latest version.

    Another possible cause of this error is serialization issues. If you are using a custom object or a complex data structure in your program and it is not properly serialized, it can cause this error. You might want to check if you are using the correct serialization method for your data structure.

    The error could also be due to file corruption. Make sure that your data file has not been corrupted. If your file has been corrupted for some reason, then you would need to re-create it before reading it again.

    Another possibility of this error is caused by the use of multiprocessing, during unpickling of data by multiple Python processes. This error can be resolved by adding to the start of your python file, immediately after you import the pickle module: “if sys.version_info[0] >= 3: ” and adding “with open(filename, ‘rb’) as pickle_file:” instead of “pickle_file = open(filename, ‘rb’)”.

    In conclusion, “pickle.UnpicklingError: invalid load key” error can be caused by various reasons that include incompatible Python versions, serialization issues, file corruption, and multiprocessing. To solve this problem, check all possible causes carefully and implement any appropriate solution.

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  2. carloshenriquehla Teacher
    2017-11-22T09:33:31+00:00Added an answer about 5 years ago

    The error “pickle.UnpicklingError: invalid load key” occurs when the data that was pickled using Python’s `pickle` module is trying to be unpickled, and the key used to encode the data cannot be found. This can happen when the data was pickled using a different version of Python or the module that created the data structure.

    To solve this issue, you can try re-pickling the data using the same version of Python and the same module. If that is not possible, you can try using a different method of serialization such as `dill` or `joblib` which can handle more complex data structures and can be used across different versions of Python.

    Another possible reason for this error is that the data was corrupted during the pickling or transmission process. In this case, you may need to discard the corrupted data and retrieve a new set of data. It is recommended to add error checking and handling to avoid such errors in the future.

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  3. steven4215 Teacher
    2017-11-17T23:25:55+00:00Added an answer about 5 years ago

    The error “pickle.UnpicklingError: invalid load key, ‘{‘” occurs when a Python pickle file is corrupted or not properly formatted. One way to resolve this is to try to locate the source of the corruption, which can be done by examining the original data that was pickled. If the data is found to be the source of the corruption, the data can be corrected or recreated and then pickled again.

    Alternatively, you can try to unpickle the file using the safe_load() function from the third-party package “joblib” instead of using the inbuilt pickle.load() function. This function might be able to unpickle files with minor errors that would otherwise cause the default pickle functions to fail.

    Another possible solution is to switch to using a different serialization format, such as JSON or YAML. These formats are more human-readable and might be easier to debug in case of errors. However, this change might require modifying the code to support the new format.

    In general, the pickle module is not guaranteed to be compatible between different versions of Python, so it is important to always use the same version of Python to pickle and unpickle data. If compatibility between different versions is required, a different serialization method should be used.

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  4. radovan.r.cvijanovic
    2017-11-29T22:01:26+00:00Added an answer about 5 years ago

    I understand that you are facing an issue with the error `Pickle.UnpicklingError: Invalid load key`. This error occurs when the pickle module is unable to find or load the object corresponding to the given key. One reason for this error could be because the pickled object was changed, renamed or deleted after some time. In such scenarios, the pickle module raises this error because it is unable to find the object corresponding to the given key.

    Another possible reason for the error could be version incompatibilities or different implementations of pickle protocol by different Python versions. In this case, you could try using a different protocol version or use more generic types when pickling your objects to avoid incompatibilities.

    To resolve the issue, you could try pickling and unpickling your objects using the same Python version, and avoid changing or renaming your objects. You could also try using a different protocol version or use more generic types when pickling your objects to avoid incompatibilities.

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