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Merged
rhettinger merged 2 commits into from
Dec 24, 2022
Merged

Misc Itertools recipe tweaks #100493

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70ccb5d
Make recipe imports explicit
rhettinger Dec 24, 2022
f756cf5
Prime factors recipe
rhettinger Dec 24, 2022
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Prime factors recipe
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@rhettinger
rhettinger committed Dec 24, 2022
commit f756cf588fc85bb7a59b48667bec98082bd13c86
44 changes: 44 additions & 0 deletions Doc/library/itertools.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -897,6 +897,21 @@ which incur interpreter overhead.
data[2] = 1
return iter_index(data, 1) if n > 2 else iter([])

def factor(n):
"Prime factors of n."
# factor(97) --> 97
# factor(98) --> 2 7 7
# factor(99) --> 3 3 11
for prime in sieve(n+1):
while True:
quotient, remainder = divmod(n, prime)
if remainder:
break
yield prime
n = quotient
if n == 1:
return

def flatten(list_of_lists):
"Flatten one level of nesting"
return chain.from_iterable(list_of_lists)
Expand Down Expand Up @@ -1251,6 +1266,35 @@ which incur interpreter overhead.
>>> set(sieve(10_000)).isdisjoint(carmichael)
True

list(factor(0))
[]
list(factor(1))
[]
list(factor(2))
[2]
list(factor(3))
[3]
list(factor(4))
[2, 2]
list(factor(5))
[5]
list(factor(6))
[2, 3]
list(factor(7))
[7]
list(factor(8))
[2, 2, 2]
list(factor(9))
[3, 3]
list(factor(10))
[2, 5]
all(math.prod(factor(n)) == n for n in range(1, 1000))
True
all(set(factor(n)) <= set(sieve(n+1)) for n in range(1, 1000))
True
all(list(factor(n)) == sorted(factor(n)) for n in range(1, 1000))
True

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

Expand Down