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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 19:47:24 -07:00
parent 2409d770d9 2876a8c272
commit c15d9e759f
1 changed files with 19 additions and 12 deletions
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31
Lib/collections.py
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@ -572,10 +572,13 @@ class Counter(dict):
if not isinstance(other, Counter): if not isinstance(other, Counter):
return NotImplemented return NotImplemented
result = Counter() result = Counter()
for elem in set(self) | set(other): for elem, count in self.items():
newcount = self[elem] + other[elem] newcount = count + other[elem]
if newcount > 0: if newcount > 0:
result[elem] = newcount result[elem] = newcount
for elem, count in other.items():
if elem not in self and count > 0:
result[elem] = count
return result return result
def __sub__(self, other): def __sub__(self, other):
@ -588,10 +591,13 @@ class Counter(dict):
if not isinstance(other, Counter): if not isinstance(other, Counter):
return NotImplemented return NotImplemented
result = Counter() result = Counter()
for elem in set(self) | set(other): for elem, count in self.items():
newcount = self[elem] - other[elem] newcount = count - other[elem]
if newcount > 0: if newcount > 0:
result[elem] = newcount result[elem] = newcount
for elem, count in other.items():
if elem not in self and count < 0:
result[elem] = 0 - count
return result return result
def __or__(self, other): def __or__(self, other):
@ -604,11 +610,14 @@ class Counter(dict):
if not isinstance(other, Counter): if not isinstance(other, Counter):
return NotImplemented return NotImplemented
result = Counter() result = Counter()
for elem in set(self) | set(other): for elem, count in self.items():
p, q = self[elem], other[elem] other_count = other[elem]
newcount = q if p < q else p newcount = other_count if count < other_count else count
if newcount > 0: if newcount > 0:
result[elem] = newcount result[elem] = newcount
for elem, count in other.items():
if elem not in self and count > 0:
result[elem] = count
return result return result
def __and__(self, other): def __and__(self, other):
@ -621,11 +630,9 @@ class Counter(dict):
if not isinstance(other, Counter): if not isinstance(other, Counter):
return NotImplemented return NotImplemented
result = Counter() result = Counter()
if len(self) < len(other): for elem, count in self.items():
self, other = other, self other_count = other[elem]
for elem in filter(self.__contains__, other): newcount = count if count < other_count else other_count
p, q = self[elem], other[elem]
newcount = p if p < q else q
if newcount > 0: if newcount > 0:
result[elem] = newcount result[elem] = newcount
return result return result