A1.10 Project: the behaviour controller

The robot starts at the bottom left, facing north (heading 0). The starter declares the constants SAFE_CM = 25, STEP_CM = 10 and DOCK_Y = 60, the exception class Docked and the abstract class Behaviour. Write: - Cruise(Behaviour): name cruise. wants() returns True when distance() is more than SAFE_CM. act() drives forward STEP_CM cm. - Sidestep(Behaviour): name sidestep. wants() returns True when distance() is SAFE_CM or less. act() moves sideways to the right, with right, by STEP_CM + 5 cm. - Dock(Behaviour): name dock. wants() returns True when the y part of position() (cm north of the start) is DOCK_Y or more. act() turns the LED green, plays one note, and raises Docked. - Controller: its constructor takes a list of behaviours in priority order and keeps them, and a step count starting at 0, in private attributes. step() goes through the behaviours in order, and for the first one whose wants() is True it adds 1 to the count, prints step <n>: <name> and calls its act(), then returns. run(max_steps) calls step() up to max_steps times inside a try block. It catches Docked and prints docked after <n> steps, and in a finally block calls stop() and prints controller stopped. The main program makes Controller([Dock(), Sidestep(), Cruise()]) and calls run(30). Do not use global or isinstance.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

SAFE_CM = 25
STEP_CM = 10
DOCK_Y = 60

class Docked(Exception):
    pass

class Behaviour:
    def __init__(self, name):
        self.name = name

    def wants(self):
        raise NotImplementedError

    def act(self):
        raise NotImplementedError

# write Cruise, Sidestep, Dock and Controller

forward(50, distance=STEP_CM)

The hint students can ask for: Get the base class and one behaviour working before the controller. The controller's job each step is the same: go through the behaviours in priority order and let the first one that wants to act do so. Docking ends the run by raising an exception, so the controller needs to catch it, and something must stop the motors however the loop ends.

A solution

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

SAFE_CM = 25
STEP_CM = 10
DOCK_Y = 60

class Docked(Exception):
    pass

class Behaviour:
    def __init__(self, name):
        self.name = name

    def wants(self):
        raise NotImplementedError

    def act(self):
        raise NotImplementedError

class Cruise(Behaviour):
    def __init__(self):
        super().__init__("cruise")

    def wants(self):
        return distance() > SAFE_CM

    def act(self):
        forward(50, distance=STEP_CM)

class Sidestep(Behaviour):
    def __init__(self):
        super().__init__("sidestep")

    def wants(self):
        return distance() <= SAFE_CM

    def act(self):
        right(50, distance=STEP_CM + 5)

class Dock(Behaviour):
    def __init__(self):
        super().__init__("dock")

    def wants(self):
        x, y = position()
        return y >= DOCK_Y

    def act(self):
        led("green")
        tone(880, 0.3)
        raise Docked()

class Controller:
    def __init__(self, behaviours):
        self.__behaviours = behaviours
        self.__steps = 0

    def step(self):
        for behaviour in self.__behaviours:
            if behaviour.wants():
                self.__steps = self.__steps + 1
                print(f"step {self.__steps}: {behaviour.name}")
                behaviour.act()
                return

    def run(self, max_steps):
        try:
            for i in range(max_steps):
                self.step()
            print("gave up")
        except Docked:
            print(f"docked after {self.__steps} steps")
        finally:
            stop()
            print("controller stopped")

controller = Controller([Dock(), Sidestep(), Cruise()])
controller.run(30)

Any program that meets the task's checks is marked correct in the simulator; this is one way, not the only way.