python 判断两个ip是不是处于同一网段

a_ip:10.10.15.100
b_ip:10.10.15.101
c_ip:10.10.10.100
netmask:255.255.255.0

def numtobinary(num):
    binary = ''
    a = int(num)
    while 1:

　　　　if a == 0 or a == 1:
    　　　　binary = '%s%s' % (str(a), binary)
    　　　　break

        num = a % 2
        binary = '%s%s' % (str(num), binary)
        a = a / 2
    binarylen = len(binary)
    binary = '%s%s' % ('0' * (8 - binarylen), binary)
    return binary

上面这个函数，是将一个 0<=x<=255的十进制数转换成二进制数。

def yu_num(ip, netmask):
    ips = ip.split('.')
    ipstr = numtobinary(ips[0]) + numtobinary(ips[1]) + numtobinary(ips[2]) + numtobinary(ips[3])
    netmasks = netmask.split('.')
    netmaskstr = numtobinary(netmasks[0]) + numtobinary(netmasks[1]) + numtobinary(netmasks[2]) + numtobinary(netmasks[3])
    ipandnetmasknum = ''
    for i in xrange(32):
        if ipstr[i] == netmaskstr[i]:
            ipandnetmasknum += ipstr[i]
        else:
            ipandnetmasknum += '0'
    return ipandnetmasknum
上面这个函数， 是获取一个ip和netmask的与的运算

a_num = yu_num(a_ip, netmask)     #a_num : '00001010000010100000111100000000'

b_num = yu_num(b_ip, netmask)     #b_num : '00001010000010100000111100000000'

c_num = yu_num(c_ip, netmask)     #c_num : '00001010000010100000101000000000'

if a_num == b_num:
　　pass
　　#是处于同一个网段

else:
　　pass
　　#不处于同一个网段