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

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Raymond Hettinger 2009-01-22 09:05:43 +00:00
parent 7bdca05a3b
commit 1bc1c8ac76
1 changed files with 5 additions and 3 deletions
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8
Lib/collections.py
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@ -253,8 +253,11 @@ class Counter(dict):
if iterable is not None: if iterable is not None:
if isinstance(iterable, Mapping): if isinstance(iterable, Mapping):
for elem, count in iterable.iteritems(): if self:
self[elem] += count for elem, count in iterable.iteritems():
self[elem] += count
else:
dict.update(self, iterable) # fast path when counter is empty
else: else:
for elem in iterable: for elem in iterable:
self[elem] += 1 self[elem] += 1
@ -280,7 +283,6 @@ class Counter(dict):
# Knuth TAOCP Volume II section 4.6.3 exercise 19 # Knuth TAOCP Volume II section 4.6.3 exercise 19
# and at http://en.wikipedia.org/wiki/Multiset # and at http://en.wikipedia.org/wiki/Multiset
# #
# Results are undefined when inputs contain negative counts.
# Outputs guaranteed to only include positive counts. # Outputs guaranteed to only include positive counts.
# #
# To strip negative and zero counts, add-in an empty counter: # To strip negative and zero counts, add-in an empty counter: