Answers

9.1 Sending

Talking to each other · Robot club · about 15 min

What this lesson is about

send(): a broadcast everyone hears; numbers into text.

• The radio
• The radio log
• Messages are text

Questions 6 marks in all

1. [1 mark]You call send("hello"). Who hears it?

   1. AEvery other robot on the mat
   2. BOnly the nearest robot
   3. COnly a robot you name
   4. DNobody until they reply
   Answer: A. There is no address. A message is a shout, not a phone call.

2. [1 mark]Which line sends your position in a way another robot can read?

   1. Asend(f"at {x:.0f},{y:.0f}")
   2. Bsend("at x,y")
   3. Csend(position())
   4. Dsend(x, y)
   Answer: A. A message is text, so the numbers must be put into the string. "at x,y" sends the letters x and y, not the numbers.

3. [1 mark]What does this program print?

   x, y = 12.6, 30.4
   print(f"at {x:.0f},{y:.0f}")

   Answer:

   at 13,30

   :.0f shows no decimal places, rounding to the nearest whole number: 12.6 becomes 13 and 30.4 becomes 30.

4. [1 mark]Two robots are not understanding each other. Where do you look first?

   1. AThe radio log under the robot view, which shows every message with its time and sender
   2. BThe depth grid
   3. CThe robot's position
   4. DThe gripper
   Answer: A. The log shows yours as well as theirs, so you can see exactly what was said and when.

5. [1 mark]You send a question. Is a reply guaranteed?

   1. ANo: the radio is a shout, and nobody has to answer
   2. BYes, every robot must reply
   3. CYes, but only from the nearest robot
   4. DOnly if you send it twice
   Answer: A. A program must cope with no answer. Lesson 9.3 adds a timeout for exactly this.

6. [1 mark]What type of Python value is every radio message?

   Answer: string. Messages are text. Numbers have to be turned into text before sending and back into numbers when received.

The task: call out

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()
# radio this to every other robot
send('hello')
# pause 1 s (the robot keeps doing what it was told)
wait(1)
print(messages())

from bugbot import *
connect()
send("hello")
forward(50, distance=20)
x, y = position()
send(f"at {x:.0f},{y:.0f}")
wait(0.5)
print(messages())