gistfile1.py

#!/usr/local/bin/python3.2

import encodings
import os
import re
import subprocess
import syslog
import sys
import time

class Network(object):
	def __init__(self, setup, prio):
		self.prio = prio
		self.setup = setup

device = "wpi0"

networks = { "Foo": Network([ "wpakey fnord" ], prio=1) }

class AccessPoint(object):
	def __init__(self, essid, bssid, signal):
		if essid[0] == "\"" and essid[-1] == "\"":
			self.essid = essid[1:-1]
		else:
			self.essid = essid
		self.bssid = bssid
		self.signal = signal

def generate_config(nw):
	if nw is None:
		return
	syslog.syslog("Configuring " + device + " for ESSID \"" + nw.essid + "\" (BSSID: " + nw.bssid + ")")

	subprocess.Popen(["ifconfig", device, "up", "bssid", nw.bssid, "nwid", nw.essid]).wait()
	for param in networks[nw.essid].setup:
		cmd = ["ifconfig", device]
		cmd.extend(param.split())
		subprocess.Popen(cmd).wait()

def select_network(aps):
	aps = list(sorted(filter(lambda x: x.essid in networks, aps), key=lambda x: (float(x.signal) * networks[x.essid].prio), reverse=True))
	return aps[0] if len(aps) != 0 else None

def connect():
	re_data = re.compile("\t\tnwid (.+) chan [0-9]+ bssid ([0-9a-f:]+) ([0-9]+)dB")

	subprocess.Popen(["ifconfig", device, "down"]).wait()
	p = subprocess.Popen(["ifconfig", device, "scan"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
	(stdout, stderr) = p.communicate(None)
	p.wait()

	aps = []
	for line in stdout.splitlines():
		m = re_data.match(encodings.utf_8.decode(line)[0])
		if m is None:
			continue
		essid = m.groups()[0]
		bssid = m.groups()[1]
		signal = m.groups()[2]

		aps.append(AccessPoint(essid, bssid, signal))

	syslog.syslog("found " + str(len(aps)) + " access point(s):")
	for n in aps: 
		syslog.syslog((" " * (2 - len(n.signal))) + n.signal + "dB: " + n.bssid + "\t" + n.essid + ("\tknown" if n.essid in networks else ""))

	generate_config(select_network(aps))
	syslog.closelog()

if __name__ == "__main__":
	if len(sys.argv) == 2:
		device = sys.argv[1]
	connect()
	time.sleep(3)