What is a facade in the context of programming and how is it used?

Design pattern that provides a unified interface to a set of interfaces in a subsystem. It defines a high-level interface that makes the subsystem easier to use.

Usage:

• Simplifies complex systems by providing a single entry point.
• Reduces coupling between the client and the subsystem, allowing internal structures to change without affecting clients.
• Provides a limited set of operations for the client, hiding implementation details.

Example:

# Subsystem
class Amplifier:
    def on(self):
        print("Amplifier on")

    def off(self):
        print("Amplifier off")

    def set_volume(self, volume):
        print(f"Amplifier volume set to {volume}")

class Tuner:
    def on(self):
        print("Tuner on")

    def off(self):
        print("Tuner off")

    def set_frequency(self, frequency):
        print(f"Tuner frequency set to {frequency}")

# Facade
class HomeTheaterFacade:
    def __init__(self, amp, tuner):
        self._amplifier = amp
        self._tuner = tuner

    def watch_movie(self, movie):
        print("Get ready to watch a movie...")
        self._amplifier.on()
        self._amplifier.set_volume(5)
        self._tuner.off() # Assume tuner is not needed for the movie

    def end_movie(self):
        print("Shutting down home theater...")
        self._amplifier.off()
        self._tuner.off()

# Client code
# amp = Amplifier()
# tuner = Tuner()
# home_theater = HomeTheaterFacade(amp, tuner)
# home_theater.watch_movie("Inception")
# home_theater.end_movie()