A Complete Example & Best Practices

This is great python knowledge. But what’s the point of the previous distinction? This is both human readable and unambigous.

can you please explain on this more:{self.class.name} For what you do that?

can you please explain here in this statement: return ‘{self.class.name}({self.color}, {self.mileage})’.format(self=self)

How i can return the statement in this way: return (‘{self.class.name} , {}, {} car’.format(self.color,self.mileage)) Is it possible?I try but i got the key error ‘self’

@Pygator - if you are refering to difference between this and previous lesson - it is mentioned that it is best practice to at least have __repr__ method. If you don’t have a __str__ method and still call it - it will fallback to __repr__ method, so you have covered both cases (str(object) and repr(object)) via just __repr__ method.

If you do need to have __str__ method on top of __repr__ e.g. for more user friendly output - that is still possible and entirely dependent on your choice.

In code above if you add following at the end of the script (not indented):

car1 = Car("Red", 10000)
print(repr(car1))
print(str(car1))

When you execute the code you get following result:

Car(Red, 10000)
Car(Red, 10000)

As you can see both methods return same result because __str__ is not defined, hence it falls back to __repr__ method. If you do define __str__ method you would get different result. Here is example of adding __str__ to code from Dan (I have made changes by using f-string instead of .format):

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

    def __repr__(self):
        return f'{self.__class__.__name__}({self.color}, {self.mileage})'

    def __str__(self):
        return f'My car color is: {self.color} and its mileage is: {self.mileage}!'


car1 = Car("Red", 10000)
print(repr(car1))
print(str(car1))

And result when you run this script is:

Car(Red, 10000)
My car color is: Red and its mileage is: 10000!

So, since both were defined, __str__ and __repr__ methods were called. And while first result gives exact code that was needed to create object (which would be useful for developer), second result (__str__ method) returns something that would be more understandable to end user who doesn’t really care what code is needed to create an object.

Hope it helps

L2I

@justpeter25x

Regarding your question: can you please explain here in this statement: return '{self.__class__.__name__}({self.color}, {self.mileage})'.format(self=self)

Please note that in Dan’s code under .format() self is defined (self=self). This is because previous self occurences in {} inside quoatation marks are not automatically recognized as self object, they are only defined within .format(self=self) part of statement.

This is how string mehtod .format() works. You cannot put variables directly in curly brackets with this method.

So, your code: return ‘{self.__class__.__name__} , {}, {} car’.format(self.color,self.mileage) when it is read by Python does not know what self in {self.__class__.__name__} is, and returns KeyError.

You do have alternative for your code to work by using f-strings (Python 3.6 and later). Since f-string allows you to call variables directly in {}, your statement would work if written like this: return f'{self.__class__.__name__}, {self.color}, {self.mileage} car'

For example, in this case if you run this script and then in console put:

car1 = Car("Red", 10000)
print(repr(car1))

Your result would be:

Car, Red, 10000 car

I am not sure if this is what you wanted to be shown, but you can work on your code from there.

Take care,

L2I

I tried to run the example. I wrote the class in a python script and ran it on the console. Unfortunately for me it doesn’t work as shown in the video. Just the print statement gives me an output, but not my_car or str(my_car).

@agerbes: If you can post a code example that’ll make it easier to figure out what’s happening. You can post it here or on Slack (#coding-questions) so we can look into it :)