Load pickled object in different file - Attribute error

Question

I have some trouble with loading a pickled file in a module that is different from the module where I pickled the file. I am aware of the following thread: Unable to load files

Answer 1

in your class_def.py file you have this code:

if __name__ == '__main__':
    doc = Document()
    utils.save_document(doc)

This means that doc will be a __main__.Document object, so when it is pickled it is expecting to be able to get a Document class from the main module, to fix this you need to use the definition of Document from a module called class_def meaning you would add an import here:

(in general you can just do from <own module name> import * right inside the if __name__ == "__main__")

if __name__ == '__main__':
    from class_def import Document 
    # ^ so that it is using the Document class defined under the class_def module
    doc = Document()
    utils.save_document(doc)

that way it will need to run the class_def.py file twice, once as __main__ and once as class_def but it does mean that the data will be pickled as a class_def.Document object so loading it will retrieve the class from the correct place. Otherwise if you have a way of constructing one document object from another you can do something like this in utils.py:

def save_document(doc):
    if doc.__class__.__module__ == "__main__":
        from class_def import Document #get the class from the reference-able module
        doc = Document(doc) #convert it to the class we are able to use


    write_file = open(file_path, 'wb')
    pickle.dump(doc, write_file)

Although usually I'd prefer the first way.

Answer 2

I had a similar problem and only just realized the differences between our implementations.

Your file structure:

• util.py
  • define pickle functions
• class_def.py
  • import util
  • define class
  • make instance
  • call save pickle
• process.py
  • import util
  • load pickle

My mistake (using your file names) was first:

• util_and_class.py
  • define class
  • define pickle funcs
  • make instance
  • call save pickle
• process.py
  • import util_and_class
  • call load pickle << ERROR

What solved my pickle import problem:

• util_and_class.py
  • define class
  • define pickle funcs
• pickle_init.py
  • import util_and_class
  • make instance
  • call save pickle
• process.py
  • call load pickle

This had the welcomed side effect that I didn't need to import the util_and_class file as it's baked into the pickle file. Calling the instance and saving the pickle in a separate file resolved the __name__ issue of "loading a pickled file in a module that is different from the module where I pickled the file."