A6.10 Project: the mission robot

Carry out a mission typed in by the user. - Ask for the mission with input("Mission? "). A valid mission matches [0-9]+(,[0-9]+)* exactly (check with re.fullmatch). While it is not valid, print invalid mission and ask again. The input box holds 3,,8 then 3,8,5, so invalid mission is printed exactly once. - For each id in the mission, in order, run the Mealy machine with a table dictionary like the one in lesson A6.2: keys (state, input), values (next_state, output), start state "SEARCH", stopping at "STOP". Each tick: sense, look up, act, change state, wait(0.1). When it reaches STOP, print reached and the id, for example reached 3. - sense(target) and act(output, steer) are written for you. sense also returns, as a third value, the list of every marker id in view on that tick. - Keep a set of every marker id seen during the whole run. At the end, print seen but not in mission: followed by the ids in the set difference, ascending, separated by single spaces, or none if it is empty. - Do not touch any marker.

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

import re

def bearing_of(cx):
    return (cx - 160) * 120 / 320      # pixels to degrees

def sense(target):
    tags = apriltags()
    ids = [t[0] for t in tags]
    mine = [t for t in tags if t[0] == target]
    if not mine:
        return "none", 0, ids
    if mine[0][3] <= 15:
        return "near", 0, ids
    return "far", bearing_of(mine[0][1]), ids

def act(output, steer):
    if output == "spin":
        turn_right(40)
    elif output == "drive":
        drive(60, 0, steer * 3)
    elif output == "halt":
        stop()

set_cv("apriltag")

The hint students can ask for: Do it in stages and test each: first the loop that keeps asking until the mission is valid; then one visit with the machine; then a loop over the ids. Add every id from each sense result to a set as you go, and at the end take away the set of mission ids.

A solution

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

import re

def bearing_of(cx):
    return (cx - 160) * 120 / 320      # pixels to degrees

def sense(target):
    tags = apriltags()
    ids = [t[0] for t in tags]
    mine = [t for t in tags if t[0] == target]
    if not mine:
        return "none", 0, ids
    if mine[0][3] <= 15:
        return "near", 0, ids
    return "far", bearing_of(mine[0][1]), ids

def act(output, steer):
    if output == "spin":
        turn_right(40)
    elif output == "drive":
        drive(60, 0, steer * 3)
    elif output == "halt":
        stop()

set_cv("apriltag")
table = {
    ("SEARCH", "none"): ("SEARCH", "spin"),
    ("SEARCH", "far"): ("APPROACH", "drive"),
    ("SEARCH", "near"): ("STOP", "halt"),
    ("APPROACH", "none"): ("SEARCH", "spin"),
    ("APPROACH", "far"): ("APPROACH", "drive"),
    ("APPROACH", "near"): ("STOP", "halt"),
}
mission = input("Mission? ")
while not re.fullmatch(r"[0-9]+(,[0-9]+)*", mission):
    print("invalid mission")
    mission = input("Mission? ")
ids = [int(part) for part in mission.split(",")]
seen = set()
for target in ids:
    state = "SEARCH"
    while state != "STOP":
        symbol, steer, in_view = sense(target)
        seen.update(in_view)
        state, output = table[(state, symbol)]
        act(output, steer)
        wait(0.1)
    print("reached", target)
extra = seen - set(ids)
print("seen but not in mission:", " ".join(str(x) for x in sorted(extra)) if extra else "none")

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