Simple SOLID Java to Python example Error-CodePudding

I'm trying to convert a example code of an eCommerce Application from Java to Python to better understand this principle.

Here is the Java code that has this example:

public class ProductCatalog {
    public void listAllProducts() {
        ProductRepository productRepository = ProductFactory.create();
        
        List<String> allProductNames = productRepository.getAllProductNames();
        
        // Display product names
    }
}

public interface ProductRepository {
    public List<String> getAllProductNames();
}

public SQLProductRepository implements ProductRepository {
    public List<String> getAllPRoductNames() {
        return Arrays.asList("soap", "toothpaste");
    }
}

public class ProductFactory {
    public static ProductRepository create() {
        return new SQLProductRepository();
    }
}

My python code is:

 import zope.interface

 class ProductRespository(zope.interface.Interface):
   def getAllProductNames(self) -> list:
     pass


 @zope.interface.implementer(ProductRespository)
 class SQLProductRepository:
   def getAllProductNames(self) -> list:
     return ["soap", "toothpaste"]


 class ProductFactory:
   def create(self) -> ProductRespository:
     return SQLProductRepository()


 class ProductCatalog:
   def listAllProducts(self) -> None:
      productRespository = ProductRespository()
      productRespository = ProductFactory.create()

      allProductNames = productRespository.getAllProductNames()
      print(allProductNames)


 myProductCatalog = ProductCatalog()
 myProductCatalog.listAllProducts()

The error is:

Traceback (most recent call last):
  File "/Users/me/udemy_courses/solid_principles/5_dependency_invertion.py", line 42, in <module>
    myProductCatalog.listAllProducts()
  File "/Users/me/udemy_courses/solid_principles/5_dependency_invertion.py", line 35, in listAllProducts
    productRespository = ProductFactory.create()
TypeError: ProductFactory.create() missing 1 required positional argument: 'self'

I guess that the problem could be in some creation of class from python or variable declaration, since this language don't need to specify the type of variable.

CodePudding user response：

In the Java code ProductFactory.create is defined as a static method.

public class ProductFactory {
    public static ProductRepository create() {  // <-- static
        return new SQLProductRepository();
    }
}

If you want to mirror that design you need to do so as well in the Python version.

class ProductFactory:
    @staticmethod
    def create() -> ProductRespository:  # note: no "self" argument
        return SQLProductRepository()

CodePudding user response：

You need to first call the class (object) and then run the function. OOP works a bit different in Python (I'm not familiar with Java but here's how python gives it a go):

class Person:
    def name(self):
        print("John")

# Person.name() → Error
Person().name() # Works

Like the above example, simply replace productRespository = ProductFactory.create() to productRespository = ProductFactory().create() and it should work. Basically, you need to call the class as well to define self.