Project Euler #50

euler50.py

from math import sqrt
from itertools import takewhile, dropwhile, count

def prime():
    primes = []
    for n in count(2):
        composite = 0
        for p in primes:
            if not n % p:
                composite = 1
                break
            elif p ** 2 > n:
                break
        if not composite:
            primes.append(n)
            yield n

def isprime(n):
    for x in range(2, int(sqrt(n)) + 1):
        if n % x == 0:
            return 0
    return 1

def csum(it):
    s = 0
    for n in it:
        s += n
        yield s

print max(j - i
            for i in takewhile(lambda  n: n < 1000000, csum(prime()))
                for j in dropwhile(lambda n: n < i,
                    takewhile(lambda  n: n < 1000000, csum(prime())))
                        if j - i < 1000000 and isprime(j - i))
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