3-tier.py

"""
*TL;DR
Separates presentation, application processing, and data management functions.
"""

fromtypingimportDict, KeysView, Optional, Union


classData:
"""Data Store Class"""

products= {
"milk": {"price": 1.50, "quantity": 10},
"eggs": {"price": 0.20, "quantity": 100},
"cheese": {"price": 2.00, "quantity": 10},
 }

def__get__(self, obj, klas):

print("(Fetching from Data Store)")
return {"products": self.products}


classBusinessLogic:
"""Business logic holding data store instances"""

data=Data()

defproduct_list(self) ->KeysView[str]:
returnself.data["products"].keys()

defproduct_information(
self, product: str
 ) ->Optional[Dict[str, Union[int, float]]]:
returnself.data["products"].get(product, None)


classUi:
"""UI interaction class"""

def__init__(self) ->None:
self.business_logic=BusinessLogic()

defget_product_list(self) ->None:
print("PRODUCT LIST:")
forproductinself.business_logic.product_list():
print(product)
print("")

defget_product_information(self, product: str) ->None:
product_info=self.business_logic.product_information(product)
ifproduct_info:
print("PRODUCT INFORMATION:")
print(
f"Name: {product.title()}, "
+f"Price: {product_info.get('price', 0):.2f}, "
+f"Quantity: {product_info.get('quantity', 0):}"
 )
else:
print(f"That product '{product}' does not exist in the records")


defmain():
"""
 >>> ui = Ui()
 >>> ui.get_product_list()
 PRODUCT LIST:
 (Fetching from Data Store)
 milk
 eggs
 cheese
 <BLANKLINE>

 >>> ui.get_product_information("cheese")
 (Fetching from Data Store)
 PRODUCT INFORMATION:
 Name: Cheese, Price: 2.00, Quantity: 10

 >>> ui.get_product_information("eggs")
 (Fetching from Data Store)
 PRODUCT INFORMATION:
 Name: Eggs, Price: 0.20, Quantity: 100

 >>> ui.get_product_information("milk")
 (Fetching from Data Store)
 PRODUCT INFORMATION:
 Name: Milk, Price: 1.50, Quantity: 10

 >>> ui.get_product_information("arepas")
 (Fetching from Data Store)
 That product 'arepas' does not exist in the records
 """


if__name__=="__main__":
importdoctest

doctest.testmod()