def pfcount(self, *sources):
sources = [self.redis_key(s) for s in sources]<EOL>with self.pipe as pipe:<EOL><INDENT>return pipe.execute_command('<STR_LIT>', *sources)<EOL><DEDENT>
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