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Add more detail to the Counter.fromkeys() comment block (GH-8124)

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Raymond Hettinger 2018-07-05 16:36:24 -07:00 committed by GitHub
parent 3ae2e33a61
commit 0c4d20bcaa
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1 changed files with 7 additions and 2 deletions
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9
Lib/collections/__init__.py
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@ -609,8 +609,13 @@ class Counter(dict):
@classmethod
def fromkeys(cls, iterable, v=None):
# There is no equivalent method for counters because setting v=1
# means that no element can have a count greater than one.
# There is no equivalent method for counters because the semantics
# would be ambiguous in cases such as Counter('aaabbc', v=2).
# Initializing counters to zero values isn't necessary because zero
# is already the default value for counter lookups. Initializing
# to one is easily accomplished with Counter(set(iterable)). For
# more exotic cases, create a dictionary first using a dictionary
# comprehension or dict.fromkeys().
raise NotImplementedError(
'Counter.fromkeys() is undefined. Use Counter(iterable) instead.')