Question

I’m learning Python OOP now and confused with somethings in the code below.

Questions:

1. def __init__(self, radius=1):
   What does the argument/attribute “radius = 1” mean exactly?
   Why isn’t it just called “radius”?

2. The method area() has no argument/attribute “radius”.
   Where does it get its “radius” from in the code?
   How does it know that the radius is 5?

   class Circle:
       pi = 3.141592
   
       def __init__(self, radius=1):
           self.radius = radius 
   
       def area(self):
           return self.radius * self.radius * Circle.pi
   
       def setRadius(self, radius):
           self.radius = radius
   
       def getRadius(self):
           return self.radius
   
   c = Circle()
   
   c.setRadius(5)
   

Also,

1. In the code below, why is the attribute/argument name missing in the brackets?

2. Why was is not written like this: def __init__(self, name)
   and def getName(self, name)?

   class Methods:
       def __init__(self):
           self.name = 'Methods'
   
       def getName(self):
           return self.name
   

Answer 1

def __init__(self, radius=1):
    self.radius = radius 

This is default value setting to initialize a variable for the class scope.This is to avoid any garbage output in case some user calls c.Area() right after c = Circle().

In the code below, why is the attribute/argument "name" missing in the brackets? 

In the line self.name = 'Methods' you are creating a variable name initialized to string value Methods.

Why was is not written like this: def init(self, name) and def
getName(self, name)?

self.name is defined for the class scope. You can get and set its value anywhere inside the class.