I have the following code:

f = urllib2.urlopen(url)
data = f.read()
f.close()

It's running on a machine with two network interfaces. I'd like to specify which interface I want the code to use. Specifically, I want it to use the one other than the one it is using by default... but I can figure out which is which if I can just pick the interface.

What's the easiest/best/most pythonic way to do this?

Not yet a complete solution, but if you were using only simple socket objects, you could do what you need this way :

import socket
s = socket.socket()
s.bind(("127.0.0.1", 0))    # replace "127.0.0.1" by the local IP of the interface to use
s.connect(("remote_server.com", 80))

Thus, you will force the system to bind the socket to the wanted network interface.