This is the fourth of five posts talking about the SOLID principles. This principles are a great guide to write good source code. Each post will talk about one of the principles:

• S Single responsability principle
• O Open/Closed principle
• L Liskov substitution principle
• I Interface segregation principle
• D Dependency inversion principle

Interface segregation principle

Its better to have many small interfaces, than a few big ones. Every code must only depend on the interfaces that directly needs and no more.

Sample

Imagine a Plane class that has some functionalities at its service: like flight control and comunications. Its better to segregate those functionalities into two separte interfaces than have only one.

class Plane:
  def __init__(self):
    self.funcs = PlaneFucntions()

class PlaneFunctions:
  def communitation1:
   // code

  def communitation2:
    // code

  def control1
    // code

It’s better to segreate complex interfaces into smaller ones:

class Plane:
  def __init__(self):
    self.controls = PlaneControls()
    self.comms = PlaneCommunications()

class PlaneControls:
  def control1
    // code

class PlaneCommunications:
  def communitation1:
   // code

  def communitation2:
    // code

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