On ‘self’ in Python

usecase

The concern is documenting the keyword self as used in python — when working within the OOP (Python w/ classes)

1. intro: on instance method

• Instance methods are methods that can be called on objects, i.e. unique instances of the class
• INSTANCE means that with this method it is possible to ACCESS UNIQUE DATA of the instantiated object of that class

If you have two objects each created from a car class, then they each may have different properties. They may have different colors, engine sizes, seats, and so on.

— https://www.makeuseof.com/tag/python-instance-static-class-methods/

• belong to the family of methods together with
• class methods (a method for the whole class)
• static methods (a method for the whole runtime)

1.1. the four rules for method names (same for variables)

1. all lower case
2. words separated by an underscore
3. non-public methods begin with a single underscore
4. if a method name needs to be mangled, two underscores may begin the name

2. CODE

""" example.py """
class ClassExample:
    def instance_method_example(self):
        return "Hello, this is your instance method"

3. instance method requirement: self parameter

• instance method must accept a reference to the instance of the class to which the method was called
• this is the keyword self as the first argument
• of course, self is just a convention as it is a parameter

4. import class from file

>>> from example import ClassExample
>>> ClassExample
<class 'example.ClassExample'>

5. instantiate an object

>>> example_object = ClassExample()
>>> example_object
<example.ClassExample object at 0x00A5AF70>

6. shorthand method call: no self parameter

• note that in this way of calling the method you are not passing the argument name for the self parameter
• check the code

class ClassExample:
    def instance_method_example(self):
        return "Hello, this is your instance method"

• check the REPL and call the method without the reference to the class at all

>>> example_object.instance_method_example()
'Hello, this is your instance method'

7. longhand method call: argument for self parameter

• the longhand format with the self passed would be

>>> ClassExample.instance_method_example(example_object)
'Hello, this is your instance method'

• here you proceed ClassName.method_name(object_name) where object_name argument stands for self parameter

8. sources

• Python Naming Conventions — CodingConvention 0 documentation