Get IP Mask from IP Address and Mask Length in Python
Question: Given an IP Address in dotted quad notation, for example:  
192.192.45.1  
And a mask length for example 8, 16, 24 typically, but could be anything i.e.
17.

Can somebody please provide the code in python to calculate the subnet mask?
Preferably I could get the result as 32-bit integer so that it is easy to hash
and then reinterpret as dotted quad when necessary for printing. I see that
python has a socket library which is basically a wrapper around the unix
socket api. I also saw it has the function inet_ntoa(), but it returns some
sort of packet struct. I'm not terribly familiar with the Python struct
library, so I was hoping some other would have some ideas. Thanks!


Answer: The simplest way is to use google's [ipaddr](https://github.com/google/ipaddr-
py) module. I assume a 25 bit mask below, but as you say, it could be anything

    
    
    >>> import ipaddr
    >>> mask = ipaddr.IPv4Network('192.192.45.1/25')
    >>> mask.netmask
    IPv4Address('255.255.255.128')
    >>>
    

The module is rather efficient at manipulating IPv4 and IPv6 addresses... a
sample of some other functionality in it...

    
    
    >>> ## Subnet number?
    >>> mask.network
    IPv4Address('192.192.45.0')
    >>>
    >>> ## RFC 1918 space?
    >>> mask.is_private
    False
    >>>
    >>  ## The subnet broadcast address
    >>> mask.broadcast
    IPv4Address('192.192.45.127')
    >>> mask.iterhosts()
    <generator object iterhosts at 0xb72b3f2c>
    

