Mention what you are trying to achieve when you ask a question. Otherwise how somebody can help you? Seeing your implementation I don't get any idea what you are trying to do. It doesn't look like something that requires a custom ModelField. Anyway the i guess the reason that it is getting called twice is, you have __metaclass__ django.db.models.SubFieldBase

which will call to_python() every time you try to set an attribute in a class which is created by metaclass SubFieldBase. In the course of execution some where as part of validation it is trying to access the 'editor_id' which will give an AttributeError, followed by a setattr on that ProfiledUserField in turn to_python gets called with a None value. I didn't investigate much so my guess might be wrong. Try using a pdb and follow the path.

PS: If you are mentioning what you want to achieve, there may be better solutions than writing custom Model Field.

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