import array
import collections
import itertools
# Placeholder constants
FREE = -1
DUMMY = -2
class Dict(collections.MutableMapping):
"Space efficient dictionary with fast iteration and cheap resizes."
@staticmethod
def _gen_probes(hashvalue, mask):
"Same sequence of probes used in the current dictionary design"
PERTURB_SHIFT = 5
if hashvalue < 0:
hashvalue = -hashvalue
i = hashvalue & mask
yield i
perturb = hashvalue
while True:
i = (5 * i + perturb + 1) & 0xFFFFFFFFFFFFFFFF
yield i & mask
perturb >>= PERTURB_SHIFT
def _lookup(self, key, hashvalue):
"Same lookup logic as currently used in real dicts"
assert self.filled < len(self.indices) # At least one open slot
freeslot = None
for i in self._gen_probes(hashvalue, len(self.indices) - 1):
index = self.indices[i]
if index == FREE:
return (FREE, i) if freeslot is None else (DUMMY, freeslot)
elif index == DUMMY:
if freeslot is None:
freeslot = i
elif (
self.keylist[index] is key
or self.hashlist[index] == hashvalue
and self.keylist[index] == key
):
return (index, i)
@staticmethod
def _make_index(n):
"New sequence of indices using the smallest possible datatype"
if n <= 2 ** 7:
return array.array("b", [FREE]) * n # signed char
if n <= 2 ** 15:
return array.array("h", [FREE]) * n # signed short
if n <= 2 ** 31:
return array.array("l", [FREE]) * n # signed long
return [FREE] * n # python integers
def _resize(self, n):
"""Reindex the existing hash/key/value entries.
Entries do not get moved, they only get new indices.
No calls are made to hash() or __eq__().
"""
n = 2 ** n.bit_length() # round-up to power-of-two
self.indices = self._make_index(n)
for index, hashvalue in enumerate(self.hashlist):
for i in Dict._gen_probes(hashvalue, n - 1):
if self.indices[i] == FREE:
break
self.indices[i] = index
self.filled = self.used
def clear(self):
self.indices = self._make_index(8)
self.hashlist = []
self.keylist = []
self.valuelist = []
self.used = 0
self.filled = 0 # used + dummies
def __getitem__(self, key):
hashvalue = hash(key)
index, i = self._lookup(key, hashvalue)
if index < 0:
raise KeyError(key)
return self.valuelist[index]
def __setitem__(self, key, value):
hashvalue = hash(key)
index, i = self._lookup(key, hashvalue)
if index < 0:
self.indices[i] = self.used
self.hashlist.append(hashvalue)
self.keylist.append(key)
self.valuelist.append(value)
self.used += 1
if index == FREE:
self.filled += 1
if self.filled * 3 > len(self.indices) * 2:
self._resize(4 * len(self))
else:
self.valuelist[index] = value
def __delitem__(self, key):
hashvalue = hash(key)
index, i = self._lookup(key, hashvalue)
if index < 0:
raise KeyError(key)
self.indices[i] = DUMMY
self.used -= 1
# If needed, swap with the lastmost entry to avoid leaving a "hole"
if index != self.used:
lasthash = self.hashlist[-1]
lastkey = self.keylist[-1]
lastvalue = self.valuelist[-1]
lastindex, j = self._lookup(lastkey, lasthash)
assert lastindex >= 0 and i != j
self.indices[j] = index
self.hashlist[index] = lasthash
self.keylist[index] = lastkey
self.valuelist[index] = lastvalue
# Remove the lastmost entry
self.hashlist.pop()
self.keylist.pop()
self.valuelist.pop()
def __init__(self, *args, **kwds):
if not hasattr(self, "keylist"):
self.clear()
self.update(*args, **kwds)
def __len__(self):
return self.used
def __iter__(self):
return iter(self.keylist)
def iterkeys(self):
return iter(self.keylist)
def keys(self):
return list(self.keylist)
def itervalues(self):
return iter(self.valuelist)
def values(self):
return list(self.valuelist)
def iteritems(self):
return itertools.izip(self.keylist, self.valuelist)
def items(self):
return zip(self.keylist, self.valuelist)
def __contains__(self, key):
index, i = self._lookup(key, hash(key))
return index >= 0
def get(self, key, default=None):
index, i = self._lookup(key, hash(key))
return self.valuelist[index] if index >= 0 else default
def popitem(self):
if not self.keylist:
raise KeyError("popitem(): dictionary is empty")
key = self.keylist[-1]
value = self.valuelist[-1]
del self[key]
return key, value
def __repr__(self):
return "Dict(%r)" % self.items()
def show_structure(self):
"Diagnostic method. Not part of the API."
print("=" * 50)
print(self)
print("Indices:", self.indices)
for i, row in enumerate(zip(self.hashlist, self.keylist, self.valuelist)):
print(i, row)
print("-" * 50)
if __name__ == "__main__":
d = Dict([("timmy", "red"), ("barry", "green"), ("guido", "blue")])
d.show_structure()
