# [Edu-sig] Kirby Urner's Sieve of Eratosthenes

**Kirby Urner
**
pdx4d@teleport.com

*Mon, 05 Jun 2000 17:27:55 -0700*

Here's an ugly way to avoid lambda -- illustrative of
points made in 'Learning Python: Nested Functions
Aren't Nested Scopes' (pg 118-120):
def erastosthenes(max): # with thanks to Ka-Ping Yee
"""Sieve of Erastosthenes"""
global sieve # force to module level
sieve = [0, 0] + [1] * max
prime = 2
while prime*prime <= max:
for i in range(prime * 2, max + 1, prime):
sieve[i] = 0
prime = prime+1 + sieve[prime+1:].index(1)
def final(x): return sieve[x] # internal function
return filter(final, range(max + 1))
Could also make
def final(x): return sieve[x]
a top-level function and eliminate this line from inside
erastosthenes().
I'm not advocating this approach -- why we have lambda is
so we can avoid it. Still, it's a useful example of
"learning Python through Python" (if not math).
Kirby