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[3.12] Improve all_equal() recipe (gh-116081) #116083

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Feb 28, 2024
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[3.12] Improve all_equal() recipe (gh-116081) #116083

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7 changes: 4 additions & 3 deletions Doc/library/itertools.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -855,10 +855,9 @@ which incur interpreter overhead.
"Given a predicate that returns True or False, count the True results."
return sum(map(pred, iterable))

def all_equal(iterable):
def all_equal(iterable, key=None):
"Returns True if all the elements are equal to each other."
g = groupby(iterable)
return next(g, True) and not next(g, False)
return len(take(2, groupby(iterable, key))) <= 1

def first_true(iterable, default=False, pred=None):
"""Returns the first true value in the iterable.
Expand Down Expand Up @@ -1217,6 +1216,8 @@ The following recipes have a more mathematical flavor:

>>> [all_equal(s) for s in ('', 'A', 'AAAA', 'AAAB', 'AAABA')]
[True, True, True, False, False]
>>> [all_equal(s, key=str.casefold) for s in ('', 'A', 'AaAa', 'AAAB', 'AAABA')]
[True, True, True, False, False]

>>> quantify(range(99), lambda x: x%2==0)
50
Expand Down