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Update comments and add an optimized path for Counter.update().

This commit is contained in:
Raymond Hettinger 2009-01-22 09:09:55 +00:00
parent 94adc8e4b5
commit dd01f8f37b
1 changed files with 5 additions and 3 deletions
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8
Lib/collections.py
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@ -255,8 +255,11 @@ class Counter(dict):
if iterable is not None:
if isinstance(iterable, Mapping):
for elem, count in iterable.items():
self[elem] += count
if self:
for elem, count in iterable.items():
self[elem] += count
else:
dict.update(self, iterable) # fast path when counter is empty
else:
for elem in iterable:
self[elem] += 1
@ -282,7 +285,6 @@ class Counter(dict):
# Knuth TAOCP Volume II section 4.6.3 exercise 19
# and at http://en.wikipedia.org/wiki/Multiset
#
# Results are undefined when inputs contain negative counts.
# Outputs guaranteed to only include positive counts.
#
# To strip negative and zero counts, add-in an empty counter: