Dependency inversion

Lesson 26 of 28 in Coddy's Clean Code - Write better code using Python course.

"Depend upon abstractions, [not] concretions."

Let's show example which violates the principle,

class LocalStorage:
	def save(self, key, value):
		print("Saved, " + key + ":" + value)

LocalStorage class saves key and value pair.

Now we have another main class which uses the LocalStorage,

class App:
	def start(self, key, value):
		storage = LocalStorage()
		storage.save(key, value)

LocalStorage is a concrete implementation and App depends on it!

The better way would be to create interface (abstract class),

from abc import ABC, abstractmethod


class Storage(ABC):
	@abstractmethod
	def save(self):
		pass

And then use instance of the interface instead of the concrete implementation.

Challenge

Easy

You are given code which is almost done, add the abstract class Storage.

Notice that after the implementation it's easy to change to other concrete class for example CloudStorage...

Try it yourself

from abc import ABC, abstractmethod


# your code here


class LocalStorage(Storage):
	def save(self, key, value):
		print("Saved, " + key + ":" + value)


class App:
	def __init__(self, storage):
		self.storage = storage

	def start(self, key, value):
		storage.save(key, value)


if __name__ == "__main__":
	storage = LocalStorage()
	app = App(storage)
	key = input()
	value = input()
	app.start(key, value)