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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_attachment_model():
 """ Returns the Attachment model that is active in this project. """


    try:
        from .models import AbstractAttachment
        klass = apps.get_model(config["attachment_model"])
        if not issubclass(klass, AbstractAttachment):
            raise ImproperlyConfigured(
                "SUMMERNOTE_CONFIG['attachment_model'] refers to model '%s' that is not "
                "inherited from 'django_summernote.models.AbstractAttachment'" % config["attachment_model"]
            )
        return klass
    except ValueError:
        raise ImproperlyConfigured("SUMMERNOTE_CONFIG['attachment_model'] must be of the form 'app_label.model_name'")
    except LookupError:
        raise ImproperlyConfigured(
            "SUMMERNOTE_CONFIG['attachment_model'] refers to model '%s' that has not been installed" % config["attachment_model"]
        )