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SENTINEL = object()
class TreeCache(object):
"""
Tree-based backing store for LruCache. Allows subtrees of data to be deleted
efficiently.
Keys must be tuples.
"""
def __init__(self):
self.root = {}
def __setitem__(self, key, value):
return self.set(key, value)
def set(self, key, value):
node = self.root
for k in key[:-1]:
node = node.setdefault(k, {})
node[key[-1]] = value
def get(self, key, default=None):
node = self.root
for k in key[:-1]:
node = node.get(k, None)
if node is None:
return default
return node.get(key[-1], default)
def clear(self):
self.root = {}
def pop(self, key, default=None):
nodes = []
node = self.root
for k in key[:-1]:
node = node.get(k, None)
nodes.append(node) # don't add the root node
if node is None:
return default
popped = node.pop(key[-1], SENTINEL)
if popped is SENTINEL:
return default
node_and_keys = zip(nodes, key)
node_and_keys.reverse()
node_and_keys.append((self.root, None))
for i in range(len(node_and_keys) - 1):
n, k = node_and_keys[i]
if n:
break
node_and_keys[i+1][0].pop(k)
return popped
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