title: Python classes self.variables
body: <p>I have started learning python classes some time ago, and there is something that I do not understand when it comes to usage of self.variables inside of a class. I googled, but couldn't find the answer. I am not a programmer, just a python hobbyist.
  Here is an example of a simple class, with two ways of defining it:</p>
  
  <p>1)first way:</p>
  
  <pre><code>class Testclass:
      def __init__(self, a,b,c):
          self.a = a
          self.b = b
          self.c = c
      def firstMethod(self):
          self.d = self.a + 1
          self.e = self.b + 2
      def secondMethod(self):
          self.f = self.c + 3
      def addMethod(self):
          return self.d + self.e + self.f
  
  myclass = Testclass(10,20,30)
  myclass.firstMethod()
  myclass.secondMethod()
  addition = myclass.addMethod()
  </code></pre>
  
  <p>2)second way:</p>
  
  <pre><code>class Testclass:
      def __init__(self, a,b,c):
          self.a = a
          self.b = b
          self.c = c
      def firstMethod(self):
          d = self.a + 1
          e = self.b + 2
          return d,e
      def secondMethod(self):
          f = self.c + 3
          return f
      def addMethod(self, d, e, f):
          return d+e+f
  
  myclass = Testclass(10,20,30)
  d, e = myclass.firstMethod()
  f= myclass.secondMethod()
  addition = myclass.addMethod(d,e,f)
  </code></pre>
  
  <p>What confuses me is which of these two is valid?
  Is it better to always define the variables inside the methods (the variables we expect to use later) as self.variables (which would make them global inside of class) and then just call them inside some other method of that class (that would be the 1st way in upper code)?
  Or is it better not to define variables inside methods as self.variables, but simply as regular variables, then return at the end of the method. And then "reimport" them back into some other method as its arguments (that would be 2nd way in upper code)?</p>
  
  <p>EDIT: just to make it clear, I do not want to define the self.d, self.e, self.f or d,e,f variables under the <strong>init</strong> method. I want to define them at some other methods like showed in the upper code.
  Sorry for not mentioning that.</p>