Python 2 to 3 Conversion

[Chris Angelico]

On Sat, Feb 17, 2018 at 4:15 PM, Wildman via Python-list
<python-list at python.org> wrote:
> I have a bit of code I found on the web that will return
> the ip address of the named network interface.  The code
> is for Python 2 and it runs fine.  But, I want to use the
> code with Python 3.  Below is the code followed by the error
> message.  Suggestions appreciated.
>
> #!/usr/bin/env python3
>
> import socket
> import fcntl
> import struct
>
> def get_ip_address(ifname):
>     s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
>     return socket.inet_ntoa(fcntl.ioctl(
>         s.fileno(),
>         0x8915,  # SIOCGIFADDR
>         struct.pack('256s', ifname[:15])
>         )[20:24])
> print(get_ip_address("eth0"))
> print(get_ip_address("lo"))
>
>
> Traceback (most recent call last):
>   File "./test.py", line 14, in <module>
>     print(get_ip_address("eth0"))
>   File "./test.py", line 12, in get_ip_address
>     struct.pack('256s', ifname[:15])
> struct.error: argument for 's' must be a bytes object

The easiest way is to encode it to ASCII:

struct.pack('256s', ifname[:15].encode('ascii'))

But you may want to see if there's a completely different way to do
what you're looking at. I'm not sure what this is doing, so I can't
advise more specifically.

ChrisA