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from pymemcache.client.murmur3 import murmur3_32
class RendezvousHash(object):
"""
Implements the Highest Random Weight (HRW) hashing algorithm most
commonly referred to as rendezvous hashing.
Originally developed as part of python-clandestined.
Copyright (c) 2014 Ernest W. Durbin III
"""
def __init__(self, nodes=None, seed=0, hash_function=murmur3_32):
"""
Constructor.
"""
self.nodes = []
self.seed = seed
if nodes is not None:
self.nodes = nodes
self.hash_function = lambda x: hash_function(x, seed)
def add_node(self, node):
if node not in self.nodes:
self.nodes.append(node)
def remove_node(self, node):
if node in self.nodes:
self.nodes.remove(node)
else:
raise ValueError("No such node %s to remove" % (node))
def get_node(self, key):
high_score = -1
winner = None
for node in self.nodes:
score = self.hash_function(
"%s-%s" % (str(node), str(key)))
if score > high_score:
(high_score, winner) = (score, node)
elif score == high_score:
(high_score, winner) = (score, max(str(node), str(winner)))
return winner
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