Python中如何使用netaddr将子网掩码转换为cidr

How use netaddr to convert subnet mask to cidr in Python

提问by Mik

How can I convert a ipv4 subnet mask to cidr notation using netaddrlibrary?
Example: 255.255.255.0 to /24

如何使用netaddr库将 ipv4 子网掩码转换为 cidr 表示法？
例子： 255.255.255.0 to /24

回答by Eugene Yarmash

Using netaddr:

使用netaddr：

>>> from netaddr import IPAddress
>>> IPAddress('255.255.255.0').netmask_bits()
24

Using ipaddressfrom stdlib:

ipaddress从 stdlib使用：

>>> from ipaddress import IPv4Network
>>> IPv4Network('0.0.0.0/255.255.255.0').prefixlen
24

You can also do it without using any libraries: just count 1-bits in the binary representation of the netmask:

您也可以在不使用任何库的情况下执行此操作：只需计算网络掩码的二进制表示中的 1 位：

>>> netmask = '255.255.255.0'
>>> sum(bin(int(x)).count('1') for x in netmask.split('.'))
24

回答by Derek Chadwell

>>> IPNetwork('0.0.0.0/255.255.255.0').prefixlen
24

回答by IAmSurajBobade

Use the following function. it is fast, reliable, and don't use any library.

使用以下功能。它快速、可靠，并且不使用任何库。

# code to convert netmask ip to cidr number
def netmask_to_cidr(netmask):
    '''
    :param netmask: netmask ip addr (eg: 255.255.255.0)
    :return: equivalent cidr number to given netmask ip (eg: 24)
    '''
    return sum([bin(int(x)).count('1') for x in netmask.split('.')])

回答by kb-0

How about this one? It does not need any additional library as well.

这个怎么样？它也不需要任何额外的库。

def translate_netmask_cidr(netmask):
    """
    Translate IP netmask to CIDR notation.
    :param netmask:
    :return: CIDR netmask as string
    """
    netmask_octets = netmask.split('.')
    negative_offset = 0

    for octet in reversed(netmask_octets):
        binary = format(int(octet), '08b')
        for char in reversed(binary):
            if char == '1':
                break
            negative_offset += 1

    return '/{0}'.format(32-negative_offset)

It is in some ways similar to IAmSurajBobade's approach but instead does the lookup reversed. It represents the way I would do the conversion manually by pen and paper.

它在某些方面类似于 IAmSurajBobade 的方法，但查找相反。它代表了我用笔和纸手动进行转换的方式。

回答by gerardw

As of Python 3.5:

从 Python 3.5 开始：

ip4 = ipaddress.IPv4Network((0,'255.255.255.0'))
print(ip4.prefixlen)
print(ip4.with_prefixlen)

will print:

将打印：

24
0.0.0.0/24

24
0.0.0.0/24