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Rework multiset methods to use less memory and to make fewer calls to __hash__.

This commit is contained in:
Raymond Hettinger 2011-04-17 19:49:29 -07:00
parent 2476ee32b1
commit 90375bc7c0
1 changed files with 19 additions and 12 deletions
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31
Lib/collections/__init__.py
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@ -601,10 +601,13 @@ class Counter(dict):
if not isinstance(other, Counter):
return NotImplemented
result = Counter()
for elem in set(self) | set(other):
newcount = self[elem] + other[elem]
for elem, count in self.items():
newcount = count + other[elem]
if newcount > 0:
result[elem] = newcount
for elem, count in other.items():
if elem not in self and count > 0:
result[elem] = count
return result
def __sub__(self, other):
@ -617,10 +620,13 @@ class Counter(dict):
if not isinstance(other, Counter):
return NotImplemented
result = Counter()
for elem in set(self) | set(other):
newcount = self[elem] - other[elem]
for elem, count in self.items():
newcount = count - other[elem]
if newcount > 0:
result[elem] = newcount
for elem, count in other.items():
if elem not in self and count < 0:
result[elem] = 0 - count
return result
def __or__(self, other):
@ -633,11 +639,14 @@ class Counter(dict):
if not isinstance(other, Counter):
return NotImplemented
result = Counter()
for elem in set(self) | set(other):
p, q = self[elem], other[elem]
newcount = q if p < q else p
for elem, count in self.items():
other_count = other[elem]
newcount = other_count if count < other_count else count
if newcount > 0:
result[elem] = newcount
for elem, count in other.items():
if elem not in self and count > 0:
result[elem] = count
return result
def __and__(self, other):
@ -650,11 +659,9 @@ class Counter(dict):
if not isinstance(other, Counter):
return NotImplemented
result = Counter()
if len(self) < len(other):
self, other = other, self
for elem in filter(self.__contains__, other):
p, q = self[elem], other[elem]
newcount = p if p < q else q
for elem, count in self.items():
other_count = other[elem]
newcount = count if count < other_count else other_count
if newcount > 0:
result[elem] = newcount
return result