is_prime.py

#! /usr/bin/env python
#coding:utf-8

"""
判断一个数是否为素数的几种方法
"""

#方法一

import math  
         
def isPrime1(n):  
    if n <= 1:  
        return False 
    for i in range(2, int(math.sqrt(n)) + 1):  
        if n % i == 0:  
            return False
        
    return True

#方法二

def isPrime2(n):
    if n <= 1:
        return False
                  
    i = 2
    while i*i <= n:
        if n % i == 0:
            return False
        i += 1
    return True

#方法三

from itertools import count

def isPrime3(n):
    if n <= 1:
        return False
    for i in count(2):
        if i * i > n:
            return True
        if n % i == 0:
            return Fals

#方法四

def isPrime4(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=isPrime4(5)
    print a