How to Define a Simple Python Class with init and repr

Define a basic Python class with an __init__ method to set instance attributes and a __repr__ method for a readable representation of objects.

Easy Python 3.9+ Aug 9, 2026 OOP & classes 15 views 0 copies

classes oop init repr

Python code

12 lines

Python 3.9+

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __repr__(self):
        return f"Person(name={self.name!r}, age={self.age!r})"


if __name__ == "__main__":
    person = Person("Alice", 30)
    print(person)

Output

stdout

Person(name='Alice', age=30)

How it works

The __init__ method is the constructor that runs when a new instance is created; it assigns the passed arguments to instance attributes name and age. The __repr__ method returns a string that represents the object, ideally one that can recreate the object when evaluated. Using !r in the f-string ensures the values are formatted using their repr(), which adds quotes around strings. When you print an object, Python calls repr if __str__ is not defined, so the output shows the custom representation.

Common mistakes

Forgetting to include `self` as the first parameter in `__init__` and other instance methods.
Returning `None` from `__repr__` or returning a non-string value.
Overriding `__repr__` but leaving `__str__` undefined, causing unexpected output when printing objects inside containers.

Variations

Use dataclasses to automatically generate `__init__` and `__repr__` methods.
Define `__str__` separately to provide a human-friendly description while keeping `__repr__` for debugging.

Real-world use cases

Modeling domain entities like customers or employees where you need clear logs of object states.
Debugging applications by seeing meaningful representations of objects in the debugger or error messages.
Storing configuration objects where the repr helps verify that values were loaded correctly.

How to Define a Simple Python Class with init and repr

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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How it works

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Variations

Real-world use cases

More from OOP & classes

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