From 3a639bbeace73d54f7e5431d3224c8c8223d81ae Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Sat, 15 Oct 2022 16:05:28 -0500 Subject: [PATCH] Improve speed. Reduce auxiliary memory to 16.6% of the main array. (GH-98294) --- Doc/library/itertools.rst | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index 056b0788a4d..88e1e5aa6ef 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -822,12 +822,13 @@ which incur interpreter overhead. 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 + data = bytearray((0, 1)) * (n // 2) + data[:3] = 0, 0, 0 limit = math.isqrt(n) + 1 for p in compress(range(limit), data): - data[p*p : n : p] = bytearray(len(range(p*p, n, p))) - return iter_index(data, 1) + data[p*p : n : p+p] = bytes(len(range(p*p, n, p+p))) + data[2] = 1 + return iter_index(data, 1) if n > 2 else iter([]) def flatten(list_of_lists): "Flatten one level of nesting"