Hardware as Objects: a gpiozero Preview

Discussion prompt

Before we open Hardware as Objects: a gpiozero Preview: without looking back, what was the main idea of Functions as Robot Decision Helpers, and what could you do by the end of it that you could not do before?

Hint: One sentence for the idea, one for the skill. If the second one is blank, that is the part to revisit.

Discussion prompt

The library robots use at camp is called gpiozero. It gives you objects with names like Robot, Motor, and DistanceSensor.

That is stated as though it always holds. Do one of two things: produce a case where it fails, or say precisely what rules such a case out. "It just does" is not on the menu.

Hint: Hunt at the extremes first — zero, one, negative, empty, equal. If every extreme survives, the reason they survive is the proof.

Match the pairs

From Today's roadmap — match each one to what it actually does. The descriptions have been shuffled.

• c1. Act
• c2. Sense
• c3. Drive

• b1. motor.forward() is a method.
• b2. sensor.distance is data.
• b3. Read, decide, go or stop.

Why: Act, Sense, Drive are easy to tell apart while they are sitting next to their descriptions and much harder afterwards, which is what this checks.

Discussion prompt

Explain A motor is an object you control by analogy to something with no Python in it at all — a queue, a recipe, a map, a bank balance, whatever fits. Then say where your analogy breaks.

Hint: An analogy that never breaks is not an analogy, it is the same idea wearing a hat. Find the seam — that is the part that is actually new.

Sort into buckets

Every line below is part of the definition of Motor or of DistanceSensor — one or the other, never both. Put each where it belongs.

Motor

An object that controls one wheel's motor.; forward() to roll it, stop() to halt it.

DistanceSensor

An object that measures how far away the nearest obstacle is.; You READ its distance attribute - no parentheses.

b1

An object that controls one wheel's motor. Methods: forward() to roll it, stop() to halt it. Called WITH parentheses.

b2

An object that measures how far away the nearest obstacle is. You READ its distance attribute - no parentheses.

Discussion prompt

Read the picture before the words. What is this showing, and what is the one thing it is built to make obvious? Commit to an answer, then read on.

Hint: Name the parts, then say what changes between them — and if nothing changes, say what is being held still.

Discussion prompt

Explain Buttons to press, gauges to read to a student a year behind you. No notation, no jargon they have not met — and it still has to be true.

Hint: If your explanation needs a symbol they have never seen, you are describing the notation rather than the idea.

Comparison matrix

From A fake gpiozero - so it runs with no robot: refill the what it is column from what you know. The rest of the table is as it appeared.

Comparison matrix

From Drive one fake motor: every row here is a choice with a cost. Fill the prints column, then say which row you would actually pick and what you give up for it.

Put in order

These are the steps of How to use any hardware object, scrambled. Put them back in order before the next slide shows you.

1. Make the object: m = Motor("left"), robot = Robot().
2. Act with a method and parentheses: m.forward(), robot.stop().
3. Sense by reading an attribute, no parentheses: sensor.distance.
4. Decide with an if on what you read, then act.

Why: This is the order the recipe itself gives. Recalling the sequence without the slide in front of you is the difference between recognising the method and being able to run it — most of what goes wrong in practice is a step done out of turn.

Discussion prompt

How to use any hardware object works on the cases you have just seen. Push it to the edge: what is the most degenerate input it still handles — empty, zero, one item, everything equal — and what is the first case where it stops being true? Name the case, not just "it breaks".

Hint: Try the smallest legal input, then the largest, then the one where two things collide. Methods are specified at their edges; the middle takes care of itself.

Discussion prompt

Explain A sensor reading is an attribute you READ to a student a year behind you. No notation, no jargon they have not met — and it still has to be true.

Hint: If your explanation needs a symbol they have never seen, you are describing the notation rather than the idea.

Discussion prompt

Explain Distance is in meters by analogy to something with no Python in it at all — a queue, a recipe, a map, a bank balance, whatever fits. Then say where your analogy breaks.

Hint: An analogy that never breaks is not an analogy, it is the same idea wearing a hat. Find the seam — that is the part that is actually new.

Predict first

A student writes this, and it looks reasonable:

You add () to the distance, as if reading the sensor were an action.

It is wrong. Say what breaks — and say it before you turn the page.

Correct: distance is a number you READ - data, like energy.

Read the gauge with no parentheses.

Why: distance is a number you READ - data, like energy. The () tells Python to call that number, which makes no sense.

Discussion prompt

The rule this trap just fixed:

Just the attribute name - Python hands back the reading, e.g. 1.0.

Now break it on purpose. Build a case that violates it and follow the consequences until something visibly fails. Where does the failure first show up — and would you have noticed it if you had not been looking?

Hint: The dangerous rules are the ones whose violation still produces an answer. If yours fails loudly, try to find one that fails quietly.

Eliminate the wrong options

Which line crashes with TypeError: 'float' object is not callable?

3 of these 4 are wrong. Strike them one at a time, and say what rules each one out before you strike the next. The survivor is the answer.

• A. sensor.distance()
• B. sensor.distance
• C. motor.forward()
• D. print(sensor.distance)

Survives elimination: A

Why: distance is data you read - it gives back a float like 1.0. Adding () tries to CALL that float, which Python refuses: 'float' object is not callable. Sense with no parentheses.

Check your understanding

Which line crashes with TypeError: 'float' object is not callable?

• A. sensor.distance() (correct)
• B. sensor.distance
• C. motor.forward()
• D. print(sensor.distance)

Answer: A

Why: distance is data you read - it gives back a float like 1.0. Adding () tries to CALL that float, which Python refuses: 'float' object is not callable. Sense with no parentheses.

Why B tempts people

sensor.distance with no () correctly reads the next reading - that's exactly how you sense, no crash.

Why C tempts people

forward is a real method, so motor.forward() is a valid call - it runs the action, no error.

Why D tempts people

print(sensor.distance) reads the float and prints it. The () belongs to print, not to distance, so it's fine.

Predict first

You write m = Motor("left"), then m.forward(). What is m, and what is forward()?

Answer it in your own words, now, with nothing to choose from. The options are on the next slide — and picking the right one off a list is an easier skill than producing it.

Correct: m is an object; forward() is a method (action) you call on it

Why: Motor("left") makes an object, just like Rover("Rex"). forward() is one of its methods - an action you call with parentheses. Same shape as everything since Lesson 1.

Check your understanding

You write m = Motor("left"), then m.forward(). What is m, and what is forward()?

• A. m is an object; forward() is a method (action) you call on it (correct)
• B. m is a function; forward is its return value
• C. m is an attribute of the Motor class you read with no parentheses
• D. forward() is data stored on m that you read like a gauge

Answer: A

Why: Motor("left") makes an object, just like Rover("Rex"). forward() is one of its methods - an action you call with parentheses. Same shape as everything since Lesson 1.

Why B tempts people

Motor(...) builds an object, not a plain function call returning a value. m is the motor object you then call methods on.

Why C tempts people

m is the object itself, not an attribute. Attributes are read FROM an object (like m.name); m is the thing you read them from.

Why D tempts people

forward() is an action you call (it prints), not data you read. Data with no () would be something like sensor.distance.

Match the pairs

Match each term to the definition this lesson gave it — not the one you would guess from the word.

• t1. Motor
• t2. DistanceSensor
• t3. Robot
• t4. driver loop

• d1. An object that controls one wheel's motor. Methods: forward() to roll it, stop() to halt it. Called WITH parentheses.
• d2. An object that measures how far away the nearest obstacle is. You READ its distance attribute - no parentheses.
• d3. An object that bundles a left and a right Motor. Its forward() and stop() drive both wheels at once.
• d4. A loop that repeatedly senses then acts: read sensor.distance, compare to a threshold, call stop() or forward(). The heartbeat of an autonomous robot.

Why: These are the working definitions of Motor, DistanceSensor, Robot, driver loop as Hardware as Objects: a gpiozero Preview uses them. Pairing them correctly is the test of whether you could state each one with the slide switched off.

Discussion prompt

if distance < 0.2: stop() else: forward(). Small distance means an obstacle is close, so play it safe and stop.

That is stated as though it always holds. Do one of two things: produce a case where it fails, or say precisely what rules such a case out. "It just does" is not on the menu.

Hint: Hunt at the extremes first — zero, one, negative, empty, equal. If every extreme survives, the reason they survive is the proof.

Comparison matrix

From One driver step: refill the value / result column from what you know. The rest of the table is as it appeared.

Predict first

A student writes this, and it looks reasonable:

Panicking that real gpiozero is a huge new thing you must memorize.

It is wrong. Say what breaks — and say it before you turn the page.

Correct: Treats the library as trivia. You'll forget it, and you'll miss that it's the same object shape you already know.

Recognize the shape; look up the names when you need them.

Why: Treats the library as trivia. You'll forget it, and you'll miss that it's the same object shape you already know.

Sort into buckets

Some of these hold up and some are the exact mistakes this lesson is built to prevent. Sort them.

Holds up

The library robots use at camp is called gpiozero. It gives you objects with names like Robot, Motor, and DistanceSensor.; Four stops, each one a piece of the same picture you already know:; A real motor spins a wheel. In code, that motor is an object: you make one and reach into it with a dot, just like the Rover.

Breaks

You add () to the distance, as if reading the sensor were an action.; Panicking that real gpiozero is a huge new thing you must memorize.

sound

These are stated as this lesson states them — each one survives the edge cases Hardware as Objects: a gpiozero Preview puts it through.

flawed

Each of these is lifted from a trap in this deck: reasonable-sounding, and wrong in a way that only shows up once you rely on it.

Predict first

In the driver loop over [1.0, 0.6, 0.15, 0.4] with if d < 0.2: stop(), on which pass does the robot STOP?

Commit to an answer, then rate it — certain, fairly sure, or guessing — and write the rating down before you turn the page.

Correct: Pass 3 (d = 0.15)

Why: 0.15 is the only reading below the 0.2 threshold, so 0.15 < 0.2 is True and stop() runs on pass 3. The other readings are all >= 0.2, so they roll forward.

The rating matters as much as the answer: confident-and-wrong is the combination that survives revision, because nothing about it feels like it needs revisiting.

Check your understanding

In the driver loop over [1.0, 0.6, 0.15, 0.4] with if d < 0.2: stop(), on which pass does the robot STOP?

• A. Pass 3 (d = 0.15) (correct)
• B. Pass 2 (d = 0.6)
• C. Pass 4 (d = 0.4)
• D. It never stops

Answer: A

Why: 0.15 is the only reading below the 0.2 threshold, so 0.15 < 0.2 is True and stop() runs on pass 3. The other readings are all >= 0.2, so they roll forward.

Why B tempts people

0.6 is bigger than 0.2, so 0.6 < 0.2 is False - the robot rolls forward on pass 2, it doesn't stop.

Why C tempts people

0.4 is also bigger than 0.2, so pass 4 rolls forward. The robot already had its close call on pass 3.

Why D tempts people

0.15 IS below 0.2, so the stop condition fires on pass 3. It does stop - just once.

Predict first

sensor = DistanceSensor([0.6]) robot = Robot() d = sensor.distance if d < 0.2: robot.stop() else: robot.forward() What prints?

Answer it in your own words, now, with nothing to choose from. The options are on the next slide — and picking the right one off a list is an easier skill than producing it.

Correct: left motor forward / right motor forward

Why: d is 0.6. 0.6 < 0.2 is False, so the else branch runs: robot.forward() fires both motors, printing left motor forward then right motor forward.

Check your understanding

sensor = DistanceSensor([0.6])
robot = Robot()
d = sensor.distance
if d < 0.2:
robot.stop()
else:
robot.forward()

What prints?

• A. left motor forward / right motor forward (correct)
• B. left motor stop / right motor stop
• C. Nothing - 0.6 doesn't match either branch
• D. TypeError: 'float' object is not callable

Answer: A

Why: d is 0.6. 0.6 < 0.2 is False, so the else branch runs: robot.forward() fires both motors, printing left motor forward then right motor forward.

Why B tempts people

stop() runs only when d < 0.2 is True. 0.6 is not below 0.2, so the if branch is skipped and forward() runs instead.

Why C tempts people

An if/else always takes exactly one branch - if the if is False, the else runs. forward() prints; nothing is silent here.

Why D tempts people

That error comes from sensor.distance() with parentheses. Here distance is read correctly with no (), so there's no crash.

Eliminate the wrong options

What's the right takeaway from this gpiozero preview?

3 of these 4 are wrong. Strike them one at a time, and say what rules each one out before you strike the next. The survivor is the answer.

• A. Recognize that motors and sensors are objects - make them, call methods, read attributes; the camp robot teaches the details
• B. Memorize every gpiozero class and method before camp, or you'll be lost
• C. gpiozero works completely differently from the Rover, so forget what you learned
• D. Sensors are called like methods: sensor.distance()

Survives elimination: A

Why: This is a familiarity preview, not a memorization test. The win is recognizing the object shape you already know - make it, call methods, read attributes - so the real robot feels familiar, not foreign.

Check your understanding

What's the right takeaway from this gpiozero preview?

• A. Recognize that motors and sensors are objects - make them, call methods, read attributes; the camp robot teaches the details (correct)
• B. Memorize every gpiozero class and method before camp, or you'll be lost
• C. gpiozero works completely differently from the Rover, so forget what you learned
• D. Sensors are called like methods: sensor.distance()

Answer: A

Why: This is a familiarity preview, not a memorization test. The win is recognizing the object shape you already know - make it, call methods, read attributes - so the real robot feels familiar, not foreign.

Why B tempts people

It's a preview for familiarity, not mastery. You look library names up; what matters is recognizing the shape, which you already have.

Why C tempts people

It's the SAME shape as the Rover - objects with methods and attributes. That's the entire point; nothing you learned is wasted.

Why D tempts people

distance is data you read with no parentheses. Calling it with () is the exact trap that crashes with 'float' object is not callable.

Step through it

Step through Milestone 2 — loop and read each pass one row at a time. What is driving the change, and what would the row after the last one be?

1. Step 1: pass is 1
2. Step 2: pass is 2
3. Step 3: pass is 3
4. Step 4: pass is 4

Comparison matrix

From Milestone 3 — add the stop condition: every row here is a choice with a cost. Fill the prints column, then say which row you would actually pick and what you give up for it.

Comparison matrix

From Milestone 4 — full driver program: refill the prints column from what you know. The rest of the table is as it appeared.

Draw it

One page, no notation unless you need it: draw how these connect — Hardware Is Just Objects · Sensing — Data Coming In · The Driver Loop · Your Turn: Maze Rover Driver. Put an arrow wherever one of them is what makes another possible, and label the arrow with why.