Hi! Who knows a more concise or equally concise but more efficient expression, which returns the same result as
[x for x in range(2,100) if not [y for y in range(2,x) if x%y==0]]
Gregor
P.S.: ... or a more beautiful one ;-)
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The fastest know way for your problem is the Eratosten sieve ...
Here's an implementation :
from sets import Set from math import sqrt
def sieve( max ):
max_val = int( sqrt( max ) )
s = Set(xrange( 4, max, 2 ))
for i in xrange( 3, max_val, 2 ):
s.update( xrange( 2*i, max, i ) )
return [ i for i in xrange( 2, max ) if i not in s ]I compared with the implementations of Gregor (optimized) and Max and here is the result :
listPrimes(100000) = 0.637619972229 (Max implementation) primeConciseOptimized(100000) = 2.9141831398 (Gregor optimized) sieve(100000) = 0.49525809288 (Eratosten sieve)
You'll just notice that Eratosten sieve is O(n) space consumption when others are less (I don't remember the density of prime numbers :o) ) were n is the maximum number you're looking for.
Pierre
-- Pierre Barbier de Reuille
INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII AMAP Botanique et Bio-informatique de l'Architecture des Plantes TA40/PSII, Boulevard de la Lironde 34398 MONTPELLIER CEDEX 5, France
tel : (33) 4 67 61 65 77 fax : (33) 4 67 61 56 68 _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
