get the IP address of a host

J Berends j.p.t.j.berends at [N0SP4M].nl
Thu Jan 6 14:35:16 CET 2005

Lee Harr wrote:

> I found that the socket solutions only work if your
> DNS entries are correct ... which in my case was not
> true. So I came up with this:

That is indeed correct, and even if the DNS entries are correct at times 
it does not give the full list of IPs by gethostbyname or gethostbyaddr.

> import commands
> ifconfig = '/sbin/ifconfig'
> # name of ethernet interface
> iface = 'eth0'
> # text just before inet address in ifconfig output
> telltale = 'inet addr:'
> ...
> Basically, it scrapes the output from ifconfig for the
> actual address assigned to the interface. Works perfectly
> on FreeBSD and Linux (given the correct configuration).

Nice way, have to device something for windows than.

 From several approached I came up with the following code:

def getipaddr(hostname='default'):
     """Given a hostname, perform a standard (forward) lookup and return
     a list of IP addresses for that host."""
     if hostname == 'default':
         hostname = socket.gethostname()
     ips = socket.gethostbyname_ex(hostname)[2]
     ips = [i for i in ips if i.split('.')[0] != '127']
     if len(ips) != 0:
         # check if we have succes in determining outside IP
         ip = ips[0]
     elif len(ips) == 0 and hostname == socket.gethostname():
         # when we want to determine local IP and did not have succes
         # with gethostbyname_ex then we would like to connect to say... 

         # and determine the local ip address bound to the
         # local socket.
             s = socket.socket()
             s.connect(('', 80))
             print ('___ connecting to internet to determine local ip')
             ip = s.getsockname()[0]
             del s
             print ('*** cannot connect to internet in order to \
                    determine outside IP address')
             raise Exception
     if len(ip) != 0:
         return ip
         print ('*** unable to determine outside IP address')
         raise Exception

It returns the IP address with which it connects to the world (not lo), 
might be a pvt LAN address or an internet routed IP. Depend on where the 
host is.

I hate the google trick actually, so any suggestions to something better 
is always welcome.

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