SRP.md

1. Single Responsibility Principle

Easy to understand. Every module, class, or function should only have a single responsibility or only one reason to change. But it’s difficult to practically implement because lines can get blurry during implementation.

To simplify this, Uncle Bob says that "This principle is about people" in this blog.

Let’s understand with an example

class Payment:
    
    # process the payment
    def process(self):
        pass
    
    # save the payment
    def save(self):
        pass
    
    # retrieve the payment information
    def retrieve(self):
        pass
    
    # return analytics data related to payment. E.g. processing time of payment
    def analytics(self):
        pass
    
    # check if the information for payment is correct or not. E.g. card number, CVV, etc
    def check(self):
        pass

As we can see, this class is performing a lot of functions for a given payment and has more than one reason to change. What if we have different people using these functionalities? If one person thinks to change the check function logic and return dict e.g {“is_cvv_valid”: True} instead of list e.g. [("is_cvv_valid", True)], this will affect the processing logic and eventually, analytics will create panic!

It will be better if each functionality is isolated and handled by a single team or individual in order to avoid any dependency and compatibility issues. Each functionality will have a standard output format. So, even if the internal logic changes for a functionality, it won’t affect the other dependent functionalities and will also have a single responsibility and reason to change. This will make the code more cohesive and easier to maintain.

class ProcessPayment:
    
    def process(self):
        pass
    
class SavePayment:
    
    def save(self):
        pass

class RetrievePayment:
    
    def retrieve(self):
        pass
    
class AnalyticsPayment:
    
    def analytics(self):
        pass
    
class SecCheckPayment:
    
    def security_check(self):
        pass