mirrors/cpython
1
0
Fork 0
mirror of https://github.com/python/cpython.git synced 2025-08-03 08:34:29 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 6

Restore early-out to factor(). Strengthen tests. (GH-100591)

Browse source
This commit is contained in:
Raymond Hettinger 2022-12-28 12:29:27 -08:00 • committed by GitHub
parent 9eca7235af
commit c4c5790120
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
1 changed files with 15 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

20
Doc/library/itertools.rst
View file

@ -901,12 +901,14 @@ 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
@ -1286,13 +1288,21 @@ 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
>>> all(set(factor(n)) <= set(sieve(n+1)) for n in range(1, 1000))
>>> 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(list(factor(n)) == sorted(factor(n)) 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(2_000))
True
>>> list(flatten([('a', 'b'), (), ('c', 'd', 'e'), ('f',), ('g', 'h', 'i')]))