Answers

0.5 Your own commands

Python quick start · Robot club · about 12 min

What this lesson is about

def, parameters and return: naming a piece of work so the program reads like what it does.

• Naming a piece of work
• Telling it how much
• Why bother

Questions 7 marks in all

1. [1 mark]What happens when Python reads the def side(): lines?

   1. ANothing yet; the lines inside run only when you call side()
   2. BThe robot drives one side straight away
   3. CThe robot drives one side, twice
   4. DPython gives an error until you call it
   Answer: A. def only gives a name to some lines. They run each time you call the name with side().

2. [1 mark]What does this program print?

   def side():
       print("drive")
       print("turn")
   
   side()
   side()

   Answer:

   drive
   turn
   drive
   turn

   Each call to side() runs both lines inside it, so two calls print drive, turn, drive, turn.

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

   def hello():
       print("hello")
   
   print("start")

   Answer:

   start

   The function is defined but never called, so its print never runs. Only print("start") does.

4. [1 mark]What does this program print?

   def side(cm):
       print("forward", cm)
   
   def square(cm):
       for i in range(4):
           side(cm)
   
   square(20)

   Answer:

   forward 20
   forward 20
   forward 20
   forward 20

   square(20) passes 20 in as cm, and the loop calls side(20) four times, one line each.

5. [1 mark]What does this program print?

   def gap_now(reading):
       return round(reading)
   
   print("the gap is", gap_now(27.6), "cm")

   Answer:

   the gap is 28 cm

   return hands a value back to where the function was called. round(27.6) is 28, so that is what gets printed.

6. [1 mark]In def side(cm):, what is cm called?

   Answer: parameter. A parameter is a name that stands for whatever the caller passes in, so side(40) makes cm 40.

7. [1 mark]Why is it worth putting a square into a square(cm) function? Choose all that apply.

   Tick every answer that is true.

   1. AThe program says what it does
   2. BA fix happens in one place, not four
   3. CYou can try that piece on its own
   4. DIt makes the robot drive more accurately
   5. EIt makes the program run faster
   Answer: A, B, C. Functions help people read, fix and test a program. The robot drives exactly the same either way.

The task: draw an L

from bugbot import *
connect()

def leg(cm):
    # drive, then turn
    forward(50, distance=cm)

leg(40)
stop()

from bugbot import *
connect()

def leg(cm):
    forward(50, distance=cm)
    turn_right(35, angle=90)

leg(40)
leg(30)
stop()