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Re^2: Perl vs. Python for prime numbers

by danaj (Friar)
on Jun 22, 2013 at 09:28 UTC ( #1040264=note: print w/replies, xml ) Need Help??

in reply to Re: Perl vs. Python for prime numbers
in thread Perl vs. Python for prime numbers

We could save typing and electrons:
use Math::Prime::Util qw/forprimes/; forprimes { say } 1000; # optionally takes range a,b
OK, it's cheating using modules. But it's easy, and it also uses a segmented sieve so should be efficient even with large values (e.g. list the primes between 10**18 and 10**18+100000), and works with bigints too.

Some Python ways to do this, all of which are *much* faster than the OP code when we want anything more than tiny values like 1000. There are probably even better ways.

Using sympy. Much slower than the Perl module:

from sympy import sieve for i in sieve.primerange(2,1000): print i

using gmpy2 (only ~2x slower than the Perl module):

import gmpy2 n = 2 while n <= 1000: print n n = gmpy2.next_prime(n)

Or some Python by hand that is very fast:

from math import sqrt, ceil def rwh_primes(n): # +ll-primes-below-n-in-python/3035188#3035188 """ Input n>=6, Returns a list of primes, 2 <= p < n """ correction = (n%6>1) n = {0:n,1:n-1,2:n+4,3:n+3,4:n+2,5:n+1}[n%6] sieve = [True] * (n/3) sieve[0] = False for i in xrange(int(n**0.5)/3+1): if sieve[i]: k=3*i+1|1 sieve[ ((k*k)/3) ::2*k]=[False]*((n/6-(k*k)/6-1)/k+1 +) sieve[(k*k+4*k-2*k*(i&1))/3::2*k]=[False]*((n/6-(k*k+4*k-2*k*( +i&1))/6-1)/k+1) sieve[n/3-correction] = False # If you want the count: return 2 + sum(sieve) return [2,3] + [3*i+1|1 for i in xrange(1,n/3-correction) if sieve +[i]] for i in rwh_primes(1000): print i

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