Passing variables creating instances self The mechanics and usage of classes need explanation

Question

I just rewrote a working program into functions in a class and everything messed up  First  in the   init   section of the class I declared a bunch of variables with self variable something  Should I be able to access modify these variables in every function of the class by using self variable in that function  In other words  by declaring self variable I have made these variables  global variables in the scope of the class right  If not  how do I handle self  Second  how do I correctly pass arguments to the class  Third  how do I call a function of the class outside of the class scope  Fouth  how do I create an Instance of the class INITIALCLASS in another class OTHERCLASS  passing variables from OTHERCLASS to INITIALCLASS  I want to call a function from OTHERCLASS with arguments from INITIALCLASS  What I ve done so far is  class OTHERCLASS        def   init   self variable1 variable2 variable3           self variable1 variable1         self variable2 variable2         self variable3 variable3     def someotherfunction self           something somecode using self variable3          self variable2 append something          print self variable2     def somemorefunctions self           self variable2 append variable1           class INITIALCLASS        def   init   self           self variable1 value1         self variable2            self variable3            self DoIt OTHERCLASS variable1 variable2 variable3       def somefunction self           variable3 Somecode          tried this         self DoIt someotherfunctions            and this         DoIt someotherfunctions    I clearly didn t understand how to pass variables to classes or how to handle self  when to use it and when not  I probably also didn t understand how to properly create an instance of a class  In general I didn t understand the mechanics of classes so please help me and explain it to me like I have no idea  which I don t  it seems   Or point me to a thorough video  or readable tutorial  All I find on the web is super simple examples  that didn t help me much  Or just very short definitions of classes and class methods instances etc  I can send you my original code if you guys want  but its quite long

User · Answer

The whole point of a class is that you create an instance  and that instance encapsulates a set of data  So it s wrong to say that your variables are global within the scope of the class  say rather that an instance holds attributes  and that instance can refer to its own attributes in any of its code  via self whatever   Similarly  any other code given an instance can use that instance to access the instance s attributes - ie instance whatever

User · Answer

So here is a simple example of how to use classes  Suppose you are a finance institute  You want your customer s accounts to be managed by a computer  So you need to model those accounts  That is where classes come in  Working with classes is called object oriented programming  With classes you model real world objects in your computer  So  what do we need to model a simple bank account  We need a variable that saves the balance and one that saves the customers name  Additionally  some methods to in- and decrease the balance  That could look like   class bankaccount        def   init   self  name  money           self name   name         self money   money      def earn money self  amount           self money    amount      def withdraw money self  amount           self money -  amount      def show balance self           print self money   Now you have an abstract model of a simple account and its mechanism  The def   init   self  name  money  is the classes  constructor  It builds up the object in memory  If you now want to open a new account you have to make an instance of your class  In order to do that  you have to call the constructor and pass the needed parameters  In Python a constructor is called by the classes s name   spidermans account   bankaccount  SpiderMan   1000    If Spiderman wants to buy M J  a new ring he has to withdraw some money  He would call the withdraw method on his account   spidermans account withdraw money 100    If he wants to see the balance he calls   spidermans account show balance     The whole thing about classes is to model objects  their attributes and mechanisms  To create an object  instantiate it like in the example  Values are passed to classes with getter and setter methods like  earn money      Those methods access your objects variables  If you want your class to store another object you have to define a variable for that object in the constructor

User · Answer

class Foo           object          class name     inherits from object      bar    Bar   Class attribute       def   init   self                       The first variable is the class instance in methods                        This is called  self  by convention  but could be any name you want             double underscore  dunder  methods are usually special   This one             gets called immediately after a new instance is created           self variable    Foo   instance attribute          print self variable  self bar    lt ---self bar references class attribute         self bar     Bar is now Baz      lt ---self bar is now an instance attribute         print self variable  self bar        def method self  arg1  arg2            This method has arguments   You would call it like this   instance method 1  2          print  in method  args     arg1  arg2         print  in method  attributes     self variable  self bar   a   Foo     this calls   init    indirectly   output                     Foo bar                    Foo  Bar is now Baz print a variable   Foo a variable    bar  a method 1  2    output                   in method  args   1 2                  in method  attributes   bar  Bar is now Baz Foo method a  1  2    lt --- Same as a method 1  2    This makes it a little more explicit what the argument  self  actually is   class Bar object       def   init   self  arg           self arg   arg         self Foo   Foo    b   Bar a  b arg variable    something  print a variable   something print b Foo variable   Foo

[python] Passing variables, creating instances, self, The mechanics and usage of classes: need explanation

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