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Merged
merged 5 commits into from
Dec 31, 2022
Merged

Improve comments in itertools uniquification recipes #100631

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af67ebe
Restore early-out to factor(). Strengthen tests.
rhettinger Dec 28, 2022
85c8f64
Improve uniquification recipes
rhettinger Dec 31, 2022
ddf5e5b
Merge branch 'main' into uniquification_recipes
rhettinger Dec 31, 2022
8d8a640
Keep the slower, but lazy solution.
rhettinger Dec 31, 2022
a3e9953
Value brevity
rhettinger Dec 31, 2022
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19 changes: 12 additions & 7 deletions Doc/library/itertools.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1019,27 +1019,30 @@ which incur interpreter overhead.
def unique_everseen(iterable, key=None):
"List unique elements, preserving order. Remember all elements ever seen."
# unique_everseen('AAAABBBCCDAABBB') --> A B C D
# unique_everseen('ABBCcAD', str.lower) --> A B C D
# unique_everseen('ABBcCAD', str.lower) --> A B c D
seen = set()
if key is None:
for element in filterfalse(seen.__contains__, iterable):
seen.add(element)
yield element
# Note: The steps shown above are intended to demonstrate
# filterfalse(). For order preserving deduplication,
# a better solution is:
# For order preserving deduplication,
# a faster but non-lazy solution is:
# yield from dict.fromkeys(iterable)
else:
for element in iterable:
k = key(element)
if k not in seen:
seen.add(k)
yield element
# For use cases that allow the last matching element to be returned,
# a faster but non-lazy solution is:
# t1, t2 = tee(iterable)
# yield from dict(zip(map(key, t1), t2)).values()

def unique_justseen(iterable, key=None):
"List unique elements, preserving order. Remember only the element just seen."
# unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
# unique_justseen('ABBCcAD', str.lower) --> A B C A D
# unique_justseen('ABBcCAD', str.lower) --> A B c A D
return map(next, map(operator.itemgetter(1), groupby(iterable, key)))

def iter_except(func, exception, first=None):
Expand Down Expand Up @@ -1371,15 +1374,17 @@ which incur interpreter overhead.

>>> list(unique_everseen('AAAABBBCCDAABBB'))
['A', 'B', 'C', 'D']

>>> list(unique_everseen('ABBCcAD', str.lower))
['A', 'B', 'C', 'D']
>>> list(unique_everseen('ABBcCAD', str.lower))
['A', 'B', 'c', 'D']

>>> list(unique_justseen('AAAABBBCCDAABBB'))
['A', 'B', 'C', 'D', 'A', 'B']

>>> list(unique_justseen('ABBCcAD', str.lower))
['A', 'B', 'C', 'A', 'D']
>>> list(unique_justseen('ABBcCAD', str.lower))
['A', 'B', 'c', 'A', 'D']

>>> d = dict(a=1, b=2, c=3)
>>> it = iter_except(d.popitem, KeyError)
Expand Down