docs: def pfcount(self, *sources):
          """
          Return the approximated cardinality of
          the set observed by the HyperLogLog at key(s).
  
          Using the execute_command because redis-py-cluster disabled it
          unnecessarily. but you can only send one key at a time in that case,
          or only keys that map to the same keyslot.
          Use at your own risk.
  
          :param sources: [str]     the names of the redis keys
          """
          sources = [self.redis_key(s) for s in sources]
          with self.pipe as pipe:
              return pipe.execute_command('PFCOUNT', *sources)