Containers and magic methods

container.py

from md5 import md5


class FakeHashRing(object):
    def __init__(self, nodes):
        self.nodes = list(nodes)

    def _hash(self, key):
        return int(md5(str(key).encode('utf-8')).hexdigest(), 16) % len(self.nodes)

    def __len__(self):
        return len(self.nodes)

    def __getitem__(self, key):
        return self.nodes[self._hash(key)]

    def __setitem__(self, key, value):
        self.nodes[self._hash(key)] = value

    def __delitem__(self, key):
        self.nodes.remove(self._hash(key))

    def __iter__(self):
        return iter(self.nodes)

    def __contains__(self, node):
        return node in self.nodes

    def remove(self, node):
        if node not in self:
            raise ValueError("node not in the ring")
        self.nodes.remove(node)

    def add(self, node):
        self.nodes.append(node)


h = FakeHashRing(["what", "a", "wonderful", "hash", "ring"])

# __len__
len(h) # 5

# __getitem__
h["foo"] # 'what'

h["bar"] #  'what'

h["baz"] # 'ring'

h[17] # 'wonderful'

# __contains__ (but __iter__ seems enough)
"what" in h
True

"bar" in h
False

# __len__ and __iter__
# (__getitem__ can substitute __iter__,
# but here we have an infinite loop because it never raises IndexError)
for node in h:
    print node
# "what", "a", "wonderful", "hash", "ring"

# __setitem__
h["foo"] = "lupo"

# __delitem__
del h["foo"]