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Itertools sieve() recipe (GH-96813) (GH-96814)

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Miss Islington (bot) 2022-09-13 19:23:30 -07:00 • committed by Pablo Galindo
parent 99f5568498
commit 6cce942bd3
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1 changed files with 6 additions and 32 deletions
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38
Doc/library/itertools.rst
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@ -314,7 +314,7 @@ loops that truncate the stream.
def count(start=0, step=1):
# count(10) --> 10 11 12 13 14 ...
# count(2.5, 0.5) -> 2.5 3.0 3.5 ...
# count(2.5, 0.5) --> 2.5 3.0 3.5 ...
n = start
while True:
yield n
@ -739,7 +739,7 @@ which incur interpreter overhead.
def prepend(value, iterator):
"Prepend a single value in front of an iterator"
# prepend(1, [2, 3, 4]) -> 1 2 3 4
# prepend(1, [2, 3, 4]) --> 1 2 3 4
return chain([value], iterator)
def tabulate(function, start=0):
@ -809,23 +809,13 @@ which incur interpreter overhead.
for k in range(len(roots) + 1)
]
def iter_index(seq, value, start=0):
"Return indices where a value occurs in a sequence."
# iter_index('AABCADEAF', 'A') --> 0 1 4 7
i = start - 1
try:
while True:
yield (i := seq.index(value, i+1))
except ValueError:
pass
def sieve(n):
"Primes less than n"
# sieve(30) --> 2 3 5 7 11 13 17 19 23 29
data = bytearray([1]) * n
data[:2] = 0, 0
limit = math.isqrt(n) + 1
for p in compress(range(limit), data):
for p in compress(count(), islice(data, limit)):
data[p+p : n : p] = bytearray(len(range(p+p, n, p)))
return compress(count(), data)
@ -866,12 +856,12 @@ which incur interpreter overhead.
def triplewise(iterable):
"Return overlapping triplets from an iterable"
# triplewise('ABCDEFG') -> ABC BCD CDE DEF EFG
# triplewise('ABCDEFG') --> ABC BCD CDE DEF EFG
for (a, _), (b, c) in pairwise(pairwise(iterable)):
yield a, b, c
def sliding_window(iterable, n):
# sliding_window('ABCDEFG', 4) -> ABCD BCDE CDEF DEFG
# sliding_window('ABCDEFG', 4) --> ABCD BCDE CDEF DEFG
it = iter(iterable)
window = collections.deque(islice(it, n), maxlen=n)
if len(window) == n:
@ -1103,6 +1093,7 @@ which incur interpreter overhead.
>>> import operator
>>> import collections
>>> import math
>>> import random
>>> take(10, count())
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
@ -1152,7 +1143,6 @@ which incur interpreter overhead.
>>> list(repeatfunc(pow, 5, 2, 3))
[8, 8, 8, 8, 8]
>>> import random
>>> take(5, map(int, repeatfunc(random.random)))
[0, 0, 0, 0, 0]
@ -1180,20 +1170,8 @@ which incur interpreter overhead.
>>> all(factored(x) == expanded(x) for x in range(-10, 11))
True
>>> list(iter_index('AABCADEAF', 'A'))
[0, 1, 4, 7]
>>> list(iter_index('AABCADEAF', 'B'))
[2]
>>> list(iter_index('AABCADEAF', 'X'))
[]
>>> list(iter_index('', 'X'))
[]
>>> list(sieve(30))
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
>>> small_primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59]
>>> all(list(sieve(n)) == [p for p in small_primes if p < n] for n in range(60))
True
>>> len(list(sieve(100)))
25
>>> len(list(sieve(1_000)))
@ -1204,14 +1182,10 @@ which incur interpreter overhead.
9592
>>> len(list(sieve(1_000_000)))
78498
>>> carmichael = {561, 1105, 1729, 2465, 2821, 6601, 8911} # https://oeis.org/A002997
>>> set(sieve(10_000)).isdisjoint(carmichael)
True
>>> list(flatten([('a', 'b'), (), ('c', 'd', 'e'), ('f',), ('g', 'h', 'i')]))
['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']
>>> import random
>>> random.seed(85753098575309)
>>> list(repeatfunc(random.random, 3))
[0.16370491282496968, 0.45889608687313455, 0.3747076837820118]