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_document(doc) 

File where the load util method is called, process.py:

import utils  if __name__ == '__main__':      utils.load_document(file_path) 

Running process.py gives the mentioned AttributeError. If I import the class_def.py file into process.py and run its main method as mentioned in the original thread it works, but I want to be able to run these two modules separately, since the class_def file is a preprocessing step that takes quite some time. How could I solve this?

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.