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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def value_from_object(self, obj):
 """ Internal Django method, used to return the placeholder ID when exporting the model instance. """

        try:
            # not using self.attname, access the descriptor instead.
            placeholder = getattr(obj, self.name)
        except Placeholder.DoesNotExist:
            return None   # Still allow ModelForm / admin to open and create a new Placeholder if the table was truncated.

        return placeholder.id if placeholder else None