When calling a function from an instance in Python, why does the parameter 'self' need to take a string or char as an argument?

Question

(I am new to Python, and I am not very good at OOP programming in general)

I have made Python programs before (Like maybe 6 or 7 small programs to test features), but I have always stayed in one file, i.e. making a class in that one Python file, and making a instance of it in the same file, and calling functions outside the classes scope. I never had to pass any arguments to any function that only had "self" as a parameter. But now I have this class here: main.py:

#"main.py" is the main script of the application; The application executes this script first;#

#IMPORT FORMAT: from FILENAME import CLASSNAME
from getBoundsForApplicationUse import getBoundsForApplicationUse; #Class is part of application.#

#Variables#
connectOrCreateServer = 2 #Will be updated with users choice; 0 = choose to host/create server; 1 = choose to connect as a client to an existing server;#

#Entry Point#
getBoundsForApplicationUse_ = getBoundsForApplicationUse; #Create instance of class "getBoundsForApplicationUse"; Check top of that specific class for information;#
getBoundsForApplicationUse_.welcomeUser(''); #Welcome the user to the application in IOStream#

As you can see, I am creating an instance of class "getBoundsForApplicationUse" from a file named "getBoundsForApplicationUse.py" (Code for that class below), which said instance is named "getBoundsForApplicationUse_" (Notice the underscoe '_' at the rear of the instance name, class and instance name are NOT identical). From this point I am calling function "welcomeUser()", which only has 'self' as a parameter: getBoundsForApplicationUse.py:

#"getBoundsForApplicationUse.py", will query the user, getting information on server or client connection for the IRC to connect; I.e, this script will get IP Address, Port Number, ask to start a server, ask to start a client, etc.#

class getBoundsForApplicationUse:

    #This function allows the user to choose to connect to a server, or host one; Should return value back to variable "connectOrCreateServer" in "main.py"; 0 = choose to host/create server; 1 = choose to connect as a client to an existing server;#
    def userChooseOption(self):

        return

    #This function welcomes the user to the application; Message created in IOStream#
    def welcomeUser(self):
        print("Welcome to ViprinIRC! A lightweight IRC chat!\n")
        return

I have to pass '', or any string of text, or else I get this error: "Traceback (most recent call last): File "E:\X-Viprin\GameCreation\AllProjects\Projects\Python\ViprinIRC\main.py", line 12, in getBoundsForApplicationUse_.welcomeUser(); #Welcome the user to the application in IOStream# TypeError: getBoundsForApplicationUse.welcomeUser() missing 1 required positional argument: 'self'"

I know that the keyword 'self' is quiet similar to keyword 'this' from java. I can use 'self' to refer to class variables and methods from this class, and other classes. For example, I could make a constructor, and I could pass 3 different integer arguments to that constructor. From there, I could use the 'self' keyword, to set the recieved arguments to class variables: "self.myClassVariableOne = myRecievedArgumentOne". I have some idea of the self keyword, but why am I needing to pass a string to the self keyword, or is something else going one, which I am not realizing? I looked up some tutorials, and entered the error into a search engine, and had trouble finding any solution.

Could someone explain what is happening here? If you can, then thank you.

....................

Answer 1

Your problem is here:

getBoundsForApplicationUse_ = getBoundsForApplicationUse; #Create instance of class "getBoundsForApplicationUse";

This doesn't create an instance of your class, it just creates another reference to the class itself.

You should be doing

getBoundsForApplicationUse_ = getBoundsForApplicationUse(); #Create instance of class "getBoundsForApplicationUse"
getBoundsForApplicationUse_.welcomeUser()

Once you've done this, welcomeUser() will receive your instance automatically as the self parameter.

Keep in mind, it was never necessary to pass a string in your code. Try passing 5, or an array. It will also work! This is because welcomeUser() is very simple and only requires you to pass something as self, but self would usually be expected to be an instance of the class.