import signal
def timeout(signum, frame):
    raise IOError, "Aaaaaah! Tempo scaduto !"
try:
    signal.signal(signal.SIGALRM, timeout)
    signal.alarm(3)       # Tempo in secondi
    mssql = _mssql.connect(host,'sa','')
    mssql.close()
    signal.alarm(0)
except IOError:
    ...