from itertools import islice
 
def integers_from(n):    # 2,3,4,...
    while True:
        yield n
        n += 1
 
def sieve(s):
    x = next(s)  
    yield x
    ps = sieve( integers_from(2))           # independent primes supply
    p = next(ps) 
    q = p*p       ; print((p,q))
    while True:
        x = next(s)
        while x<q: 
            yield x
            x = next(s)
        # here x == q
        s = filter(lambda y,p=p: y % p, s)  # filter creation postponed 
        p = next(ps)                        #   until square of p seen in input
        q = p*p     
 
print( list( islice( sieve( integers_from(2)), 19990, 20000) )) 
 
  # http://i...content-available-to-author-only...e.com/kYh7Di (non-postponed):         this:
  # 390-400   0.11s  9.8MB                                  1000:  0.07s  9.6MB
  # 590-600   0.18s 10.2MB                                 10000:  0.34s  9.6MB  20k:0.80s-9.6M
  # 890-900   0.34s 10.5MB                                100000:  6.96s  9.6MB   n^1.3   !!! (optimal TD)
  # 990-1000   **run-time error: signal: 25 (SIGXFSZ)**   150000: 11.71s 10.3MB   n^1.3   

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