Simple SOLID Java to Python example Error

Question

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.

Answer 1

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.