8000 [3.11] Restore early-out to factor(). Strengthen tests. (GH-100591) by miss-islington · Pull Request #100592 · python/cpython · GitHub
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[3.11] Restore early-out to factor(). Strengthen tests. (GH-100591) #100592

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Merged
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Dec 28, 2022
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[3.11] Restore early-out to factor(). Strengthen tests. (GH-100591) #100592

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20 changes: 15 additions & 5 deletions Doc/library/itertools.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -862,12 +862,14 @@ which incur interpreter overhead.
"Prime factors of n."
# factor(99) --> 3 3 11
for prime in sieve(math.isqrt(n) + 1):
while n >= prime:
while True:
quotient, remainder = divmod(n, prime)
if remainder:
break
yield prime
n = quotient
if n == 1:
return
if n >= 2:
yield n

Expand Down Expand Up @@ -1256,13 +1258,21 @@ which incur interpreter overhead.
[3, 3]
>>> list(factor(10))
[2, 5]
>>> list(factor(999953*999983))
>>> list(factor(128_884_753_939)) # large prime
[128884753939]
>>> list(factor(999953 * 999983)) # large semiprime
[999953, 999983]
>>> all(math.prod(factor(n)) == n for n in range(1, 1000))
>>> list(factor(6 ** 20)) == [2] * 20 + [3] * 20 # large power
True
>>> list(factor(909_909_090_909)) # large multiterm composite
[3, 3, 7, 13, 13, 751, 113797]
>>> math.prod([3, 3, 7, 13, 13, 751, 113797])
909909090909
>>> all(math.prod(factor(n)) == n for n in range(1, 2_000))
True
>>> all(set(factor(n)) <= set(sieve(n+1)) for n in range(1, 1000))
>>> all(set(factor(n)) <= set(sieve(n+1)) for n in range(2_000))
True
>>> all(list(factor(n)) == sorted(factor(n)) for n in range(1, 1000))
>>> all(list(factor(n)) == sorted(factor(n)) for n in range(2_000))
True

>>> list(flatten([('a', 'b'), (), ('c', 'd', 'e'), ('f',), ('g', 'h', 'i')]))
Expand Down
0