How should I pass variables between functions in this class?

Question

What I'm trying to do: executing the script, I will have to type in two numbers and it will compare them. I want to be asked a total of 3 times. The first time I will type in 10 and 5, second time 5 and 10 and the third time I will type in 10 and 10 to get all three possible answers.

My problem with the first code is: getnumbers() is being called inside of Checknumbers(). I want to create functions and a loop and strictly ONLY execute the functions inside a dedicated loop and not within another function.

I want everything clean cut and no reference of any function inside another function, I don't want to use any global variables either.

I solved this with a class but I'm not really sure if I'm butchering the language or if this is common practice. Also I have to reference the class inside the checknumbers() function.

First solution:

def getnumbers():
    x = input("Enter the X number: ")
    y = input("Enter the Y number: ")
    return x, y

def checknumbers():
    x, y=getnumbers()
    if   x > y:
        print(f'x is larger then y: x is {x} and y is {y}')
    elif y > x:
        print(f"y is larger then x: x is {x} and y is {y}")
    elif y == x:
        print(f"x is equal to y: x is {x} and y is {y}")     
    else:
        print("Dont know mate")


n = 0
while(n < 3):
    checknumbers()
    n += 1

This is the variant with the class:

class ui:
    x = input("Enter the X number: ")
    y = input("Enter the Y number: ")


def checknumbers():
    if   ui.x > ui.y:    
        print(f'x is larger then y: x is {ui.x} and y is {ui.y}')
    elif ui.y > ui.x:
        print(f"y is larger then x: x is {ui.x} and y is {ui.y}")
    elif ui.y == ui.x:
        print(f"x is equal to y: x is {ui.x} and y is {ui.y}")     
    else:
        print("Dont know mate")

n = 0
while(n < 3):
    checknumbers()
    n += 1

Ideal solution, so both functions getnumbers() and checknumbers are clean cut independent of each other and they are being called inside the while loop, the problem is that x and y from the getnumbers() function are unknown to checknumbers.

The requirement is: I cant have any reference to any other function inside my functions, how do I pass x and y without referencing them?:

def getnumbers():
    x = input("Enter the X number: ")
    y = input("Enter the Y number: ")
    return x, y

def checknumbers():
    if   x > y:
        print(f'x is larger then y: x is {x} and y is {y}')
    elif y > x:
        print(f"y is larger then x: x is {x} and y is {y}")
    elif y == x:
        print(f"x is equal to y: x is {x} and y is {y}")     
    else:
        print("Dont know mate")


n = 0
while(n < 3):
    getnumbers()
    checknumbers()
    n += 1

Answer 1

If you don't want to call getnumbers() within checknumbers(), the only alternative that makes sense is to pass the numbers as parameters to checknumbers().

def getnumbers():
    x = int(input("Enter the X number: "))
    y = int(input("Enter the Y number: "))
    return x,y

def checknumbers(x, y):
    if x > y:
        # etc.

...

for _ in range(3):
    x,y = getnumbers()
    checknumbers(x,y)

That at least has better separation of concerns.

Answer 2

• You're getting confused between classes and instances, and between class attributes and instance attributes. (Read e.g. this)
  • The OO way to store state variables (like x,y) so you don't have to pass them around between function(/method) calls is to make them instance attributes. (Not class attributes, as you were doing. Don't worry, I did that too when I first learned Python).
  • So we declare a class UI; we will access its instance attributes as self.x, self.y inside its methods.
  • Don't try to directly do stuff on class UI. You must instantiate it first: ui = UI(). You should follow the Python convention that class names are Uppercase/CamelCase: UI, instance names are lowercase e.g. ui, ui1, ui2...
  • You were trying to put code directly into the class definition of UI, not define methods and put the code in that, and your UI class didn't even have an __init__()
  • Methods are functions inside a class, they always have a first argument self. If they didn't, the method wouldn't be able to access the rest of the class(!)
• Now that we cleared that up, there are a couple of ways to decompose the methods to do what you want to do:
  1. Have an empty __init__() (you could just make its body do pass). Have get_numbers() and check_numbers() be separate methods, which you manually call in-order. This is what I show below and is closest to what you said you want ("I want no reference to any function inside another function"), but is bad decomposition - what if the client called check_numbers() before get_numbers()? It would blow up on TypeError since __init__() initializes x,y with None.
  2. Better would be to have __init__() call the method get_numbers() under-the-hood to guarantee the instance gets properly initialized. (We could always call get_numbers() again later if we want to input new numbers). That's easy to change, I leave that to you.
  3. In approach 1., we had to initialize the instance members to something (otherwise trying to access them in check_numbers() will blow up). So we initialize to None, which will deliberately throw an exception if we compare. It doesn't really matter, this is just bad decomposition to not have __init__() properly initialize the instance (and call whatever methods it needs to to get that done). That's why approach 2. is better. Generally you should always have an __init__() that initializes the class into a known state, so that any other method can safely be called.

Code:

class UI:
    def __init__(self, x=None, y=None):
        self.x = x
        self.y = y
    def get_numbers(self):
        self.x = input("Enter the X number: ")
        self.y = input("Enter the Y number: ")
    def check_numbers(self):
        """This is bad decomposition because if the client calls check_numbers() before get_numbers(), the NoneType will throw a TypeError"""
        if   self.x > self.y:    
            print(f'x is larger then y: x is {self.x} and y is {self.y}')
        elif self.y > self.x:
            print(f'y is larger then x: x is {self.x} and y is {self.y}')
        elif self.y == self.x:
            print(f'x is equal to y: x is {self.x} and y is {self.y}')     
        else:
            print("Don't know mate")

# Declare an instance and reuse it three times    
ui = UI()
for n in range(3):
    ui.get_numbers()
    ui.check_numbers()

Also, some minor stylistic points:

• you don't need a while-loop for a simple counter: n = 0, while(n < 3) ... n += 1 . A for-loop is a one-liner: for n in range(3):
• good Python style (see PEP-8) is to name the methods lower_case_with_underscores, thus get_numbers(), check_numbers()
• a great top-down way to design a class is to write its method signatures first, think about what methods and attributes you'll need and how they'll work together. Example: "get_numbers() will get the user input, hence we'll need attributes self.x,y to store the numbers so check_numbers() can access them". And this way you should hit any problems with class design before you've written a wall of code.

Answer 3

• I don't see anything wrong with the first solution (except for the fact that getumbers returns strings in Python 3) . Classes are not the solution for every problem

• I cant have any reference of any other function inside my functions, how do I pass x and y without referencing them?

  It's impossible to pass something without referencing it. Even if x and y were global variables (which is much worse than your current design) the using function would need to reference them.

I don't understand why you are under the impression that calling a function inside another function is bad or wrong design.