10. String representations of objects: str() vs repr()

str() and repr() are builtin functions used to represent the object in the form of string.

Suppose we have an object x.

str(x) would be calling the dunder (double underscore) __str__ method of x as x.__str__()

repr(x) would be calling the dunder (double underscore) __repr__ method of x as x.__repr__()

😑 Well, what all are these new terms __str__ and __repr__ 🤔?

As we know that Python is object oriented language, and so supports inheritance. In Python, all the classes would inherit from the base class object. object class has the methods __str__, __repr__ and a lot more (which can be deepdived in some other notebook 😉). Hence every class would be having __str__ and __repr__ implicitly 😊

Python’s official documentations states that __str__ should be used to represent a object which is human readable(informal), whereas __repr__ is used for official representation of an object.

from datetime import datetime

now = datetime.now()

print(f"The repr of now is: {repr(now)}")
print(f"The str of now is: {str(now)}")

The repr of now is: datetime.datetime(2024, 5, 2, 8, 39, 55, 954969)
The str of now is: 2024-05-02 08:39:55.954969

class ProgrammingLanguage:
    def __init__(self, language: str):
        self.language = language


language_obj = ProgrammingLanguage(language="Python")
print(f"The repr of language_obj is: {repr(language_obj)}")
print(f"The str of language_obj is: {str(language_obj)}")

The repr of language_obj is: <__main__.ProgrammingLanguage object at 0x7747cfceb6d0>
The str of language_obj is: <__main__.ProgrammingLanguage object at 0x7747cfceb6d0>

In the above example we see that default repr output. The address of the object might be different for everyone.

Now let’s try to override the __str__ and __repr__ methods and see how the representations work

class Human:
    def __init__(self, name: str, age: int):
        self.name = name
        self.age = age

    # overriding __str__ method
    def __str__(self):
        return f"I am {self.name} of age {self.age}"

    # overriding __repr__ method
    def __repr__(self):
        return f"Human(name={self.name}, age={self.age}) object at {hex(id(self))}"


human_obj = Human(name="IronMan", age=48)
print(f"The repr of human_obj is: {repr(human_obj)}")
print(f"The str of human_obj is: {str(human_obj)}")

The repr of human_obj is: Human(name=IronMan, age=48) object at 0x7747cfd23a50
The str of human_obj is: I am IronMan of age 48

We see that the result representations of the human_obj have been changed as we have overridden the __str__ and __repr__ methods 😊