CODEWITHSUNDEEP
pythonoopliskov-substitution-principle
mr_incredible
mr_incredible

Reputation: 1135

The Liskov substitution principle

I'm reading the book "Learning Python Design Patterns" written by Chetan Giridhar and I came across a design principle called the Liskov substitution principle, which states that derived classes must be able to completely substitute the base (parent) class.

I don't think I understand this, because what's the point of writing a derived class if it can completely replace the base class? Doesn't it make the base class redundant?

From my understanding and experience derived classes extend functionality of the base class hence should be dependent on the base class.

What the author is trying to help me understand?

Upvotes: 0

Views: 511

Answers (1)

Sarmad Sohail
Sarmad Sohail

Reputation: 275

Derived classes should extend without replacing the functionality of old classes. Which means derived classes should be substitutable for their parent/base classes. Moreover, they can be usable in the place of their parent classes without any unexpected behavior.

We can't replace the parent class's functionality but we can re-write it in the child class and for modification extend that child class onwards. It will keep us from the chain reaction that might occur in complex software by changing the parent class so we opt to duplicate it in child class and then write our desired modifications.

Upvotes: 1

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