Bridge Exercise 2: The M×N Problem Appears

What changed since Exercise 1

The smart-home app is growing. Two things happened:

New devices were added: Thermostat and Speaker.

New remote behaviors were added: alongside low and high intensity, there is now a ScheduledRemote that turns a device on at a given level for a set duration, then turns it off automatically.

If you hadn’t used Bridge in Exercise 1, your class list would now look like this:

LowIntensityLight
HighIntensityLight
ScheduledLight

LowIntensityFan
HighIntensityFan
ScheduledFan

LowIntensityThermostat
HighIntensityThermostat
ScheduledThermostat

LowIntensitySpeaker
HighIntensitySpeaker
ScheduledSpeaker

That’s 12 classes for 3 remotes × 4 devices — and you’d write most of the same logic over and over.

With Bridge, you need to add:

Thermostat    (1 new class)
Speaker       (1 new class)
ScheduledRemote  (1 new class)

Three new classes total. Every combination works automatically.

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Part A — Add the new devices

Extend the system from Exercise 1 with two new concrete implementors.

Thermostat

set_level(level) interprets the level as a target temperature in degrees. Level 30 means 30°C, level 90 means 90°F… keep it simple, just store and print the value.

Print: "Thermostat set to {level}°" when set_level is called. Print: "Thermostat on" / "Thermostat off" for power. status() returns e.g. "Thermostat: ON, level=22".

Speaker

set_level(level) controls volume.

Print: "Speaker volume set to {level}%" when set_level is called. Print: "Speaker on" / "Speaker off" for power. status() returns e.g. "Speaker: ON, level=45".

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Part B — Add ScheduledRemote

ScheduledRemote takes a device, a level, and a duration in seconds. When toggle_power() is called:

1. It turns the device on at the given level.
2. It prints how long the device will stay on.
3. It does not actually wait (no time.sleep — just simulate by printing).
4. It then immediately turns the device off and prints a confirmation.

class ScheduledRemote(RemoteControl):
    def __init__(self, device: Device, level: int, duration_seconds: int):
        ...

Expected output for ScheduledRemote(speaker, level=60, duration_seconds=30).toggle_power():

Speaker on
Speaker volume set to 60%
[Scheduled] Will turn off after 30 seconds
Speaker off

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Part C — Verify all combinations work

After implementing Parts A and B, all nine combinations should work without any changes to the existing remote classes:

devices  = [Light(), Fan(), Thermostat(), Speaker()]
remotes  = [LowIntensityRemote, HighIntensityRemote]

for DeviceClass in [Thermostat, Speaker]:
    device = DeviceClass()
    r = LowIntensityRemote(device)
    r.toggle_power()
    print(device.status())
    r.toggle_power()

And:

speaker = Speaker()
scheduled = ScheduledRemote(speaker, level=60, duration_seconds=30)
scheduled.toggle_power()

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Skeleton

See exercise2.py. It imports everything from exercise_solution1.py so you only need to add the new classes.

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Things to think about

• When you add Thermostat, do you need to touch LowIntensityRemote at all?
• When you add ScheduledRemote, do you need to touch Light or Fan at all?
• That independence is exactly what Bridge is buying you.

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Exercise 1 · Exercise 3