Added type hints to 3-tier structural pattern

Author: rednafi

patterns/structural/3-tier.py

@@ -3,68 +3,77 @@
 Separates presentation, application processing, and data management functions.
 """
 
+from typing import Dict, KeysView, Optional, Type, TypeVar, Union
+
+T = TypeVar("T")
+
 
 class Data:
     """ Data Store Class """
 
     products = {
-        'milk': {'price': 1.50, 'quantity': 10},
-        'eggs': {'price': 0.20, 'quantity': 100},
-        'cheese': {'price': 2.00, 'quantity': 10},
+        "milk": {"price": 1.50, "quantity": 10},
+        "eggs": {"price": 0.20, "quantity": 100},
+        "cheese": {"price": 2.00, "quantity": 10},
     }
 
-    def __get__(self, obj, klas):
+    def __get__(
+        self, obj: Optional[T], klas: Type[T]
+    ) -> Dict[str, Dict[str, Dict[str, Union[int, float]]]]:
+
         print("(Fetching from Data Store)")
-        return {'products': self.products}
+        return {"products": self.products}
 
 
 class BusinessLogic:
     """ Business logic holding data store instances """
 
     data = Data()
 
-    def product_list(self):
-        return self.data['products'].keys()
+    def product_list(self) -> KeysView[str]:
+        return self.data["products"].keys()
 
-    def product_information(self, product):
-        return self.data['products'].get(product, None)
+    def product_information(
+        self, product: str
+    ) -> Optional[Dict[str, Union[int, float]]]:
+        return self.data["products"].get(product, None)
 
 
 class Ui:
     """ UI interaction class """
 
-    def __init__(self):
+    def __init__(self) -> None:
         self.business_logic = BusinessLogic()
 
-    def get_product_list(self):
-        print('PRODUCT LIST:')
+    def get_product_list(self) -> None:
+        print("PRODUCT LIST:")
         for product in self.business_logic.product_list():
             print(product)
-        print('')
+        print("")
 
-    def get_product_information(self, product):
+    def get_product_information(self, product: str) -> None:
         product_info = self.business_logic.product_information(product)
         if product_info:
-            print('PRODUCT INFORMATION:')
+            print("PRODUCT INFORMATION:")
             print(
-                'Name: {0}, Price: {1:.2f}, Quantity: {2:}'.format(
-                    product.title(), product_info.get('price', 0), product_info.get('quantity', 0)
-                )
+                f"Name: {product.title()}, "
+                + f"Price: {product_info.get('price', 0):.2f}, "
+                + f"Quantity: {product_info.get('quantity', 0):}"
             )
         else:
-            print('That product "{0}" does not exist in the records'.format(product))
+            print(f"That product '{product}' does not exist in the records")
 
 
 def main():
     ui = Ui()
     ui.get_product_list()
-    ui.get_product_information('cheese')
-    ui.get_product_information('eggs')
-    ui.get_product_information('milk')
-    ui.get_product_information('arepas')
+    ui.get_product_information("cheese")
+    ui.get_product_information("eggs")
+    ui.get_product_information("milk")
+    ui.get_product_information("arepas")
 
 
-if __name__ == '__main__':
+if __name__ == "__main__":
     main()
 
 ### OUTPUT ###