Project Euler #10 (Python)

Question

Why is my algorithm for finding the sum of all prime numbers below 2 million so slow? I\'m a fairly beginner programmer and this is what I came up with for finding the solution:

Answer 1

sum = 2

def isPrime(n):
    if n % 2 == 0: return False
    for i in range(3, int(n**0.5)+1, 2):
        if n % i == 0: return False
    return True
if __name__ == "__main__":
    n = 1
    while n < 2000000:
        n += 2
        if isPrime(n):sum += n
print sum