from datetime import datetime
d1=datetime.now()
def eratosthenes():
        '''Yields the sequence of prime numbers via the Sieve of Eratosthenes.'''
        D = {}  # map composite integers to primes witnessing their compositeness
        q = 2   # first integer to test for primality
        while 1:
                if q not in D:
                        yield q        # not marked composite, must be prime
                        D[q*q] = [q]   # first multiple of q not already marked
                else:
                        for p in D[q]: # move each witness to its next multiple
                                D.setdefault(p+q,[]).append(p)
                        del D[q]       # no longer need D[q], free memory
                q += 1
suma=0
for i in eratosthenes():
        if i>2000000:
                break
        suma+=i
print(suma)
print (datetime.now()-d1)

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