{: .note }

Language: English | [O'zbek]({{ site.baseurl }}/uz/04-isp/)

Clients should not be forced to depend on interfaces they do not use.

Large, monolithic interfaces should be split into smaller, focused ones. A class should only implement the methods that are relevant to its behavior.

In violation.py a fat Worker interface forces every implementor to provide work(), eat(), and sleep():

class Worker(ABC):
    @abstractmethod
    def work(self) -> str: ...

    @abstractmethod
    def eat(self) -> str: ...

    @abstractmethod
    def sleep(self) -> str: ...

A Robot has no concept of eating or sleeping, yet it is forced to implement those methods:

class Robot(Worker):
    def eat(self) -> str:
        raise NotImplementedError("Robots don't eat")

    def sleep(self) -> str:
        raise NotImplementedError("Robots don't sleep")

In correct.py the fat interface is split into three focused interfaces:

Each class implements only what it needs:

class Human(Workable, Eatable, Sleepable):
    ...

class Robot(Workable):  # no eat() or sleep() required
    def work(self) -> str:
        return f"Robot {self.model} is working"

A function that only needs workers accepts Workable — it does not pull in unused eat() or sleep() contracts.