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Does this look like a good way to use a class?


I have a class, and a Python script that calls functions from the class.

The class is called User_Input_Test. The script is called input_test.py.

input_test.py will request input from the user by using one of the class functions/methods: get_user_input(self). It is then supposed to print out whatever the user entered, through the use of the second function/method called show_output(self).

It generates an error:

User_Input_Test.show_output()\
  File "/Users/michel/Python_Projects/User_Input_Test.py", line 49, in show_output\
    """)
AttributeError: type object 'User_Input_Test' has no attribute 'brand'

It looks like show_output(self) is not able to see the data pulled in from the user via get_user_input(self).

Would you say that is the correct interpretation of the error? And most importantly: Is there a solution for this, or am I trying to use a class for something it was never designed for?

user_input.py:

from User_Input_Test import User_Input_Test
import time

#User_Input_Test.__init__(self, name, brand, engine, doors, fuel_type, aircon, weight, mpg, tax)

print("This little application collects data about your car")
print("Please fill out the following questionnaire:")
uname = input("What is your first name?:")
User_Input_Test.get_user_input()

print(f"{uname}, these are your car's attributes: ")
time.sleep(2)

User_Input_Test.show_output()

User_Input_Test.py

class User_Input_Test:
    """
    Small Class that asks the user for their car attributes and can print them out
    Attributes:
        brand(string)
        engine(string)
        ....
    """

    def __init__(self, brand, engine, doors, fuel_type, aircon, weight, mpg, tax):
        self.brand = brand
        self.engine = engine
        self.doors = doors
        self.fuel_type = fuel_type
        self.aircon = aircon
        self.weight = weight
        self.mpg = mpg
        self.tax = tax

    @classmethod
    def get_user_input(self):
        while 1:
            try:
                brand = input("What is the Brand & Model of your car? (e.g. 'Mercedes Benz, E-Class'):    ")
                engine = input("Engine Cylinders and Displacement (e.g. '4 Cylinders, 2.1 Liters'):    ")
                doors = input("How many doors does it have?:    ")
                fuel_type = input("What fuel does it use? (e.g. Petrol, Diesel, LPG):    ")
                aircon = input("Does it have Airconditioning? (Yes/No):    ")
                weight = input("How much does it weight in KG? (e.g. 1800kg):    ")
                mpg = input("What is the fuel consumption in Imperial MPG? (e.g. 38mpg):    ")
                tax = input("How much does the UK Roadtax cost per year? (e.g. £20):    ")
                return self(brand,engine,doors,fuel_type,aircon,weight,mpg,tax)
            except:
                print('Invalid input!')
                continue
            
    def show_output(self):
        print(f"""
==========================================================================
    Brand Name:.......................  {self.brand}
    Engine:...........................  {self.engine}
    Number of Doors:..................  {self.doors}
    Fuel Type used by the engine:.....  {self.fuel_type}
    Does it have Aircon?:.............  {self.aircon}
    Fuel consumption in Imperial MPG:.  {self.mpg}
    Cost of Road Tax per Year:........  {self.tax}
==========================================================================
        """)

Solution

  • User_Input_Test.show_output() tries to call show_output on the class itself; you need to call it on the instance returned by User_Input_Test.get_user_input().

    from User_Input_Test import User_Input_Test
    import time
    
    print("This little application collects data about your car")
    print("Please fill out the following questionnaire:")
    uname = input("What is your first name?:")
    car = User_Input_Test.get_user_input()
    
    print(f"{uname}, these are your car's attributes: ")
    time.sleep(2)
    
    car.show_output()
    

    Note: check out PEP 8, the Python style guide, notably the naming conventions for modules and classes. In this case, I would name the module car and the class Car for more clarity and better style. Also, the argument to a classmethod is usually named cls, as self is conventionally reserved for the instance in normal methods.