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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 _get_form(self, config_name, only_required=False):
 """Get form for given config else create form"""

        if getattr(self, config_name, None):
            return import_object_by_string(getattr(self, config_name))

        def use_field(field):
            if not only_required:
                return True
            return field.default == NOT_PROVIDED

        return modelform_factory(self.model, fields=[f.name for f in self.model.get_fields() if use_field(f)])