Python 3.9 is now generally available.

google.appengine.api.memcache.delete_multi

Delete multiple keys at once.

keys List of keys to delete.
seconds Optional number of seconds to make deleted items 'locked' for 'add' operations. Value can be a delta from current time (up to 1 month), or an absolute Unix epoch time. Defaults to 0, which means items can be immediately added. With or without this option, a 'set' operation will always work. Float values will be rounded up to the nearest whole second.
key_prefix Prefix to put on all keys when sending specified keys to memcache. See docs for get_multi() and set_multi().
namespace a string specifying an optional namespace to use in the request.

True if all operations completed successfully. False if one or more failed to complete.