Further information#

How to pronounce the double underscore?#

The double underscore used in magic methods like __init__ or __repr__ is pronounced “dunder”.

What is the self variable for?#

In methods the first variable is used to refer to the instance of a given class. It is conventional to use self.

As an example let us consider this class:

class PetDog:
    """
    A class for a Pet.

    Has two methods:
        - `bark` which returns "Woof" as a string.
        - `give_toy` which gives a toy to the dog in question. This updates the
          `toys` attribute.
    """

    def __init__(self):
        self.toys = []

    def bark(self):
        """
        Returns the string Woof.
        """
        return "Woof"

    def give_toy(self, toy):
        """
        Updates the instances toys list.
        """
        self.toys.append(toy)

If we now create two dogs:

auraya = PetDog()
riggins = PetDog()

Both have no toys:

auraya.toys

[]

riggins.toys

[]

Now when we want to give riggins a toy we need to specify which of those two empty lists to update:

riggins.give_toy("ball")
riggins.toys

['ball']

However auraya still has no toys:

auraya.toys

[]

When running riggins.give_toy("ball"), internally the give_toy method is taking self to be riggins and so the line self.toys.append(toy) in fact is running as riggins.toys.append(toy).

The variable name self is a convention and not a functional requirement. If we modify it (using inheritance):

class OtherPetDog(PetDog):
    """
    A class for a Pet.

    Has two methods:
        - `bark` which returns "Woof" as a string.
        - `give_toy` which gives a toy to the dog in question. This updates the
          `toys` attribute.
    """

    def give_toy(the_dog_in_question, toy):
        """
        Updates the instances toys list.
        """
        the_dog_in_question.toys.append(toy)

Then we get the same outcome:

riggins = OtherPetDog()
riggins.toys

[]

riggins.give_toy("ball")
riggins.toys

['ball']

Indeed the line the_dog_in_question.toys.append(toy) is run as riggins.toys.append(toy).

You should however use self as it is convention and helps with readability of your code.

Why do we use CamelCase for classes but snake_case for functions?#

This is specified by the Python convention: https://www.python.org/dev/peps/pep-0008/

These conventions are important as it helps with readability of code.

What is the difference between a method and a function?#

A method is a function defined on a class and always takes a first argument which is the specific instance from which the method is called.

Other resources on objects#