How can I do DNS lookups in Python, including referring to /etc/hosts?

The normal name resolution in Python works fine. Why do you need DNSpython for that. Just use socket's getaddrinfo which follows the rules configured for your operating system (on Debian, it follows /etc/nsswitch.conf:

>>> print(socket.getaddrinfo('google.com', 80))
[(10, 1, 6, '', ('2a00:1450:8006::63', 80, 0, 0)), (10, 2, 17, '', ('2a00:1450:8006::63', 80, 0, 0)), (10, 3, 0, '', ('2a00:1450:8006::63', 80, 0, 0)), (10, 1, 6, '', ('2a00:1450:8006::68', 80, 0, 0)), (10, 2, 17, '', ('2a00:1450:8006::68', 80, 0, 0)), (10, 3, 0, '', ('2a00:1450:8006::68', 80, 0, 0)), (10, 1, 6, '', ('2a00:1450:8006::93', 80, 0, 0)), (10, 2, 17, '', ('2a00:1450:8006::93', 80, 0, 0)), (10, 3, 0, '', ('2a00:1450:8006::93', 80, 0, 0)), (2, 1, 6, '', ('209.85.229.104', 80)), (2, 2, 17, '', ('209.85.229.104', 80)), (2, 3, 0, '', ('209.85.229.104', 80)), (2, 1, 6, '', ('209.85.229.99', 80)), (2, 2, 17, '', ('209.85.229.99', 80)), (2, 3, 0, '', ('209.85.229.99', 80)), (2, 1, 6, '', ('209.85.229.147', 80)), (2, 2, 17, '', ('209.85.229.147', 80)), (2, 3, 0, '', ('209.85.229.147', 80))]

I'm not really sure if you want to do DNS lookups yourself or if you just want a host's ip. In case you want the latter,

/!\ socket.gethostbyname is deprecated, prefer socket.getaddrinfo

from man gethostbyname:

The gethostbyname*(), gethostbyaddr*(), [...] functions are obsolete. Applications should use getaddrinfo(3), getnameinfo(3),

import socket
print(socket.gethostbyname('localhost')) # result from hosts file
print(socket.gethostbyname('google.com')) # your os sends out a dns query