python实现判断素数

import math

def is_prime_1(n):
    if n <= 1:
        return False
    for i in range(2, int(math.sqrt(n) + 1)):
        if n % i == 0:
            return False
    return True

def is_prime_2(n):
    if n <= 1:
        return False
    i = 2
    while i * i <= n:
        if n % i == 0:
            return False
        i += 1
    return True

from itertools import count

def is_prime_3(n):
    if n <= 1:
        return False
    for i in count(2):
        if i * i > n:
            return True
        if n % i == 0:
            return False

def is_prime_4(n):
    if n <= 1:
        return False
    if n == 2:
        return True
    if n % 2 == 0:
        return False
    i = 3
    while i * i <= n:
        if n % i == 0:
            return False
        i += 2
    return True

if __name__ == '__main__':
    a = [1, 2, 3, 4]
    import sys
    for i in a:
        res = 'is_prime_%s' % i
        print(getattr(sys.modules['__main__'], res)(19))