Facade

One simple door.

The Facade pattern gives you a single, easy front door to a complicated system. Rather than making callers coordinate many classes, you offer one object with a few high-level methods that do the orchestration behind the scenes.

Example: a HomeTheaterFacade.watchMovie() turns on the projector, dims the lights, powers the amplifier, and starts the player — the caller just calls one method.

# Problem: client must orchestrate a noisy subsystem by hand.
encoder = VideoEncoder()
encoder.set_codec("h264")
encoder.set_bitrate(4000)
audio = AudioMixer()
audio.normalize(track)
uploader = CdnClient()
uploader.put(encoder.encode(file), audio.mix())
# Every caller repeats this ritual — and breaks when internals change.

# Fix: Facade offers one simple method over the subsystem.
class VideoFacade:
    def publish(self, file, track):
        # Hide encoder / mixer / CDN wiring behind one door.
        encoder = VideoEncoder()
        encoder.set_codec("h264")
        encoder.set_bitrate(4000)
        audio = AudioMixer().normalize(track)
        CdnClient().put(encoder.encode(file), audio)

# Clients only know publish() — subsystem can be refactored freely.
VideoFacade().publish("clip.mp4", "voice.wav")

Decoupling clients from subsystems.

The Facade wraps a subsystem's classes and delegates client requests to the right components. Clients depend only on the facade, reducing coupling to the many moving parts inside.

• Doesn't hide the subsystem — advanced clients can still use subsystem classes directly when needed.
• Reduces learning curve — a small, task-oriented API over a large subsystem.
• Layering — facades often mark the entry point of a subsystem layer.

Boundaries and relations.

• vs Adapter — Facade defines a new, simpler interface over many objects; Adapter makes an existing object match a specific expected interface.
• Law of Demeter — facades help clients avoid reaching deep into subsystem internals.
• Risk: god object — a facade can grow into a bloated do-everything class; keep it focused, or provide several role-specific facades.
• Often a Singleton — a subsystem usually needs only one facade instance.