import time
def avancer():
    return "avancer"

def tg():
    return "tg"

def robot_obstacle():
    return False

def robot_execute(s):
    print "execution de l'ordre : ", s

# /!\ variable globale
env = {'obstacle': False}

def main():
    yield "debut de main"
    for i in range(10):
        while not env["obstacle"]:
            yield avancer()
        yield tg()

env["callback"] = TODO_COMPLETER

def main_loop(callback):
    print callback.next()
    for i in range(1000):
        env['obstacle'] = robot_obstacle()
        time.sleep(1)
        ordre_robot = TODO_COMPLETER
        robot_execute(ordre_robot) # execture un ordre
    print 'fin de la boucle evt'

main_loop(env["callback"])