def __init__(self, *args, **kwargs):
super(SetUsernameSerializer, self).__init__(*args, **kwargs)<EOL>username_field = User.USERNAME_FIELD<EOL>self.fields['<STR_LIT>' + username_field] = self.fields.pop(username_field)<EOL>
This method should probably be replaced by a better solution.
Its purpose is to replace USERNAME_FIELD with 'new_' + USERNAME_FIELD
so that the new field is being assigned a field for USERNAME_FIELD