How is .format(self=self) used?

Question

I saw a piece of code that was like this:

class Car:
    def __init__(self,color,mileage):
        self.color = color
        self.mileage = mileage

    def __str__(self):
        return 'a {self.color} car'.format(self=self)

my_car = Car('blue', 13585)
print(my_car)

How does the self=self that is used in the str method work?

Answer 1

def __str__(self):
        return 'a {self.color} car'.format(self=self)

The first self in self=self refers to what the format function will change in your string. For example, it could also be

'a {obj.color} car'.format(obj=self)

The left-hand side self in self=self refers to the actual value that will be input. In this case, the object passed as argument. In other words, it could also be

def __str__(obj):
        return 'a {self.color} car'.format(self=obj)

Thus, for an overall view, you have

def __str__(value_passed):
        return 'a {value_to_change.color} car'.format(value_to_change=value_passed)

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Now why to use self?

It is just a convention used in python programming. Python passes to its instance methods automatically an object that is a pointer to itself. Can also check this question for further info