How to Test a class and its method

Question

New to Python, Got an error that i am unsure how to fix. Trying to answer a home work question. I am a bit confused on how to test the class and its methods, Which is part 2 of the question. Is there a special way of doing it?

Write a class to represent a Product as per following specifications:

Class name: Product (note uppercase "P")

Define instance attributes as specified by the items in dictionary object product2 i.e. discontinued, lead_time_days, etc.

Define an init() method which initialises the instance attributes to the value of the parameters passed to the method

Define a set_product_name() method which sets the product_name in the instance variable to the value of the parameter passed

Define a get_product_details() method which returns the product details formatted as "product_name - product_description"

After having defined the class, you need to test the class and its methods to show that it works. You can do this as follows:

Instantiate an object of the class (name it prod) and pass product2 to the initialiser (pass the whole product2 object, not individual attributes)

Set the product_name to something different by calling set_product_name() and passing it an appropriate parameter

Call get_product_details() to get the product name and description (and print it)

Code:

product2 = {
 "discontinued": 0,
 "lead_time_days": 4,
 "product_category": "Personal Computers",
 "product_description": "8 inch Display (1920x1200) ...",
 "product_id": 104,
 "product_name": "NVIDIA SHIELD Tablet (WiFi)",
 "reorder_level": 10,
 "unit_price": 299.0
}
# My Code
class Product:
 def __init__(self, discontinued, lead_time_days, product_category, product_description, product_id, product_name, reorder_level, unit_price):
 self.discontinued = discontinued
 self.product_category = product_category
 self.product_description = product_description
 self.product_id = product_id
 self.product_name = product_name
 self.reorder_level = reorder_level
 self.unit_price = unit_price
 def set_product_name(self, value):
 self.product_name = value
 def get_product_details(self):
 return self.product_name + " " + self.product_description

Edit 1

I tried this but i know its wrong.

prod = Product(product2["discontinued"], product2["product_category"], product2['product_description'], product2['product_id'], product2['product_name'],product2['reorder_level'],product2['unit_price'])
prod.set_product_name('star')
print ('get_product_details'())

• David Freeman: You don't show your whole code so we can't see how you are creating the object. Try something like (2 lines) x = Product(0, 4, 'Personal Computers', '8 inch', 104, 'Nvidia', 10, 299.0) and then print product.get_product_details()
• Rikio: Edited my original post, not sure if that will help.

Answer 1

Pro tip: use unpacking to deliver keyword arguments to a class method.

This can be done by changing your class to the following:

class Product:
 def __init__(self, discontinued=None, lead_time_days=None, product_category=None, product_description=None, product_id=None, product_name=None, reorder_level=None, unit_price=None):
 self.discontinued = discontinued
 self.product_category = product_category
 self.product_description = product_description
 self.product_id = product_id
 self.product_name = product_name
 self.reorder_level = reorder_level
 self.unit_price = unit_price
 def set_product_name(self, value):
 self.product_name = value
 def get_product_details(self):
 return self.product_name + " " + self.product_description

By giving your arguments default values (e.g. discontinued=None) it makes them keyword arguments. This is helpful if you have a dictionary or a large number of inputs to a function.

To create the object/instantiate the class you can call:

obj = Product(**product2)

**product2 basically means:

discontinued=0,lead_time_days=4,product_category="Personal Computers",product_description="8 inch Display (1920x1200) ...",product_id=104,product_name="NVIDIA SHIELD Tablet (WiFi)",reorder_level=10,unit_price=299.0

After the object is instantiated you call its methods using dot notation:

obj.set_product_name('new name')
print(obj.get_product_details())

• PeptideWitch: Whoa. That's amazing, I didn't know you could do that with dictionary keys. What happens if there isn't a 1 for 1 match between the class keywords and the dict keys? Will it do as many as possible, or will it error out?

Answer 2

product2 can be passed as kwargs dict.

Then you can call your function for the instance you created:

prod = Product(**product2)
prod.set_product_name('star')
print (prod.get_product_details())
star 8 inch Display (1920x1200) ...

Answer 3

1. Your testing code doesn't comply to the requirement "pass the whole product2 object, not individual attributes". You pass individual attributes:

prod = Product(product2["discontinued"], product2["product_category"], product2['product_description'], product2['product_id'], product2['product_name'],product2['reorder_level'],product2['unit_price'])

2. The setattr(object, name, value) function will be handy in your case.

My solution:

product2 = { 
 "discontinued": 0,
 "lead_time_days": 4,
 "product_category": "Personal Computers",
 "product_description": "8 inch Display (1920x1200) ...",
 "product_id": 104,
 "product_name": "NVIDIA SHIELD Tablet (WiFi)",
 "reorder_level": 10, 
 "unit_price": 299.0
}
class Product:
 def __init__(self, specification):
 for key, value in specification.items():
 setattr(self, key, value) 
 def set_product_name(self, value):
 self.product_name = value
 def get_product_details(self):
 return f'{self.product_name} - {self.product_description}'
###Test
# Instantiate an object of the class (name it prod) and pass product2 to
# the initialiser (pass the whole product2 object, not individual attributes)
prod = Product(product2)
# Set the product_name to something different by calling set_product_name()
# and passing it an appropriate parameter
prod.set_product_name('Another Tablet')
# Call get_product_details() to get the product name and
# description (and print it)
print(prod.get_product_details())