Select the most suitable Memcached backend based on the config and
        on what's installed

def set_memcached_backend(self, config):
        """
        Select the most suitable Memcached backend based on the config and
        on what's installed
        """
        # This is the preferred backend as it is the fastest and most fully
        # featured, so we use this by default
        config['BACKEND'] = 'django_pylibmc.memcached.PyLibMCCache'
        if is_importable(config['BACKEND']):
            return
        # Otherwise, binary connections can use this pure Python implementation
        if config.get('BINARY') and is_importable('django_bmemcached'):
            config['BACKEND'] = 'django_bmemcached.memcached.BMemcached'
            return
        # For text-based connections without any authentication we can fall
        # back to Django's core backends if the supporting libraries are
        # installed
        if not any([config.get(key) for key in ('BINARY', 'USERNAME', 'PASSWORD')]):
            if is_importable('pylibmc'):
                config['BACKEND'] = \
                        'django.core.cache.backends.memcached.PyLibMCCache'
            elif is_importable('memcached'):
                config['BACKEND'] = \
                        'django.core.cache.backends.memcached.MemcachedCache'