testing for a network connection

[DeaD_EyE]

Don't try to solve it with checking everything before.
Work with timeouts. Set the timeout to your socket, then it will throw a socket.timeout exception if you try to read a file and the read took longer than the timeout.

import socket


def read(fd):
    try:
        fd.read(1)
    except socket.timeout:
        print("Read timed out")


s = socket.socket()
s.settimeout(10) # 10 seconds
s.connect(("google.com", 80))
f = s.makefile()

# will fail
read(f)

Regular files won't throw a socket.timeout.
I hope this is a better answer.

By the way, how do you check if a socket is still connected?
I think there is no safe method.