<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_backend(self):
 """ Returns the associated cache backend. """

        try:
            cache = caches[machina_settings.ATTACHMENT_CACHE_NAME]
        except InvalidCacheBackendError:
            raise ImproperlyConfigured(
                'The attachment cache backend ({}) is not configured'.format(
                    machina_settings.ATTACHMENT_CACHE_NAME,
                ),
            )
        return cache