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note to self

The importance of self

To confirm: when you define a class you are, in effect, defining a custom factory
function that you can then use in your code to create instances:

The target identifier that holds a = Athlete() Invoke the class’s custom factory
function.
a reference to your instance

When Python processes this line of code, it turns the factory function call into
the following call, which identifies the class, the method (which is automatically
set to __init__()), and the object instance being operated on:

The name of the class
The target identifier

Athlete().__init__(a) of the object instance

The name of the method

Now take another look at how the __init__() method was defined in the
class:

def __init__(self):

# The code to initialize an "Athlete" object.
...

Check out what Python turns your object creation invocation into. Notice
anything?

The target identifer is assigned to the self argument.
This is a very important argument assignment. Without it, the Python interpreter
can’t work out which object instance to apply the method invocation to. Note
that the class code is designed to be shared among all of the object instances:
the methods are shared, the attributes are not. The self argument helps
identify which object instance’s data to work on.

192 Chapter 6