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How and When to Use .__repr__()

Dan Bader
Pythonic OOP String Conversion: .__repr__() vs .__str__() Dan Bader 01:22

In this lesson, you’ll see how to use a second dunder method that controls how ojects are converted to strings, the .__repr__():

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

    def __repr__(self):
        return '__repr__ for Car'

    def __str__(self):
        return '__str__ for Car'

You’ll learn when __repr__ is used and how it is different from .__str__(). The next lesson will cover the differences between the two in more detail.

00:00 In order to understand what’s going on here, I defined this class—or, kind of, redefined my Car class. And what this new version of the Car class does, it actually has a .__repr__() and a .__str__() implementation.

00:16 Now, those implementations are just dummy implementations that are going to tell us what’s going on behind the scenes. So, if something calls .__repr__() behind the scenes, we’re going to get '__repr__ for Car' as a result, and if something calls .__str__(), we’re going to get '__str__ for Car' as a result.

00:30 So now, we can walk through to the same example again and do a print(my_car). And you can see here, okay, it called the .__str__() function.

00:39 We could also go through the .format() example again—you can see it called the .__str__() function. And now, if we do my_car and just inspect that, we can see here that it’s actually called .__repr__() for the Car.

00:50 And another way to force this is to call the built-in repr() function, and then that’s going to do the right thing and call the correct .__repr__() implementation for this.

01:03 Usually, you just want to use the str() and repr() helpers for that.

01:09 Now, of course, the big question is, “Okay, so now we have these two—what’s actually the difference between them, or what’s the different use cases where you would use them?”

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