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 using pickle and multipile modules. I've tried the proposed solution of importing the class into the module where I am unpickling my file, but it keeps giving me the same error: `AttributeError: Can't get attribute 'Document' on <module '__main__' from ''> ` The basic structure of what I am trying to do: Util file that pickles and unpickles objects, utils.py: ``` import pickle def save_document(doc): from class_def import Document write_file = open(file_path, 'wb') pickle.dump(doc, write_file) def load_document(file_path): from class_def import Document doc_file = open(file_path, 'rb') return pickle.load(doc_file) ``` File where Document object is defined and the save util method is called, class_def.py: ``` import utils class Document(object): data = "" if __name__ == '__main__': doc = Document() utils.save_do…

Accepted Answer

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.

Load pickled object in different file - Attribute error

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