Finding Pythagorean triples

import itertools
from math import sqrt
import time
import random

def generateTriples( lim, a = 3, b = 4, c = 5 ):
    h = max( a, b, c )
    if h > lim:
        return
    i = 1
    while i * h <= lim:
        yield ( a * i, b * i, c * i )
        i += 1

    for x in generateTriples(lim,  a - 2*b + 2*c,  2*a - b + 2*c,  2*a - 2*b + 3*c):
        yield x
    for x in generateTriples(lim,  a + 2*b + 2*c,  2*a + b + 2*c,  2*a + 2*b + 3*c):
        yield x
    for x in generateTriples(lim, -a + 2*b + 2*c, -2*a + b + 2*c, -2*a + 2*b + 3*c):
        yield x

def countTriplesFrom( n ):
    s = set( c * c for c in n )
    count = 0

    for ( a, b ) in itertools.combinations( n, 2 ):
        c = a * a + b * b
        if c in s:
            #print ( a, b, sqrt( c ) )
            count += 1
    return count

def countTriplesFrom_fast( n ):
    s = set( n )
    l = max( n )
    count = 0

    for ( a, b, c ) in generateTriples( l ):
        if ( a in s ) and ( b in s ) and ( c in s ):
            #print ( a, b, c )
            count += 1

    return count

def trial( f, n, numTrials ):
    start = time.clock()
    for t in xrange( numTrials ):
        f( n )
    end = time.clock()
    return ( end - start ) * 1.0 / numTrials

L = 2000000
N = 6000
X = random.sample( xrange( 1, L + 1 ), N )
T = 3

from sys import setrecursionlimit
setrecursionlimit(2000)

print "L=",L,"N=",N
print "O(N^2)", trial( countTriplesFrom, X, T )
print "O(L log L)", trial( countTriplesFrom_fast, X, T )