Understanding Python’s __repr__ Method

The __repr__ method is a special method in Python that is used to define a string representation for an object. It is intended to provide a clear and unambiguous representation of the object, primarily for debugging and development purposes. This is also called dunder method because of the double underscores before and after the name.

Without __repr__, when you print an object or inspect it in an interactive session, python will use a default representation that includes the object’s type and memory address, which is often not very informative. That’s where __repr__ comes in handy.

Why Do We Need __repr__?

Without __repr__, printing or inspecting an object shows only the default representation:

class MyCustomClass:
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

    def full_name(self):
        return f"{self.first_name} {self.last_name}"

custom_obj = MyCustomClass("John", "Doe")
print(custom_obj)  # Default representation without __repr__

The output will be something like:

<__main__.MyCustomClass at 0x1f045501d50>

This output tells you very little—it shows only the type and memory address.

Making Objects More Informative

To provide a more informative representation, you can implement the __repr__ method in your class:

class MyCustomClass:
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

    def full_name(self):
        return f"{self.first_name} {self.last_name}"
    
    def __repr__(self):
        return f"MyCustomClass(first_name='{self.first_name}', last_name='{self.last_name}')"

custom_obj = MyCustomClass("John", "Doe")
print(custom_obj)  # Now uses the __repr__ method

The output will be:

MyCustomClass(first_name='John', last_name='Doe')

Now the output clearly shows the object’s state, which is much more useful when debugging.

Whenever you call repr(custom_obj), it will return the string defined in the __repr__ method. This will common for all python objects, including built-in types like lists, dictionaries, and tuples, which have their own __repr__ implementations that provide useful information about their contents.

How __repr__ Helps in Debugging

Imagine you are debugging a program with a list of custom objects:

students = [
    MyCustomClass("Alice", "Smith"),
    MyCustomClass("Bob", "Johnson")
]
print(students)

Output with __repr__:

[MyCustomClass(first_name='Alice', last_name='Smith'),
 MyCustomClass(first_name='Bob', last_name='Johnson')]

This gives you an immediate snapshot of the list contents, saving time compared to printing each attribute manually. For example if you already familiar with django models, the __repr__ method is often used to provide a concise summary of model instances, which is invaluable during development and debugging.

Beyond __repr__: Rich Representations in Jupyter

In Jupyter notebooks, we have additional capabilities to customize the representation of objects using special methods like _repr_html_, _repr_json_, _repr_svg_, etc., which allow for rich representations in different formats.

For example, you may seen from scikit-learn library, when you create a model and display it in a Jupyter notebook, it often shows a nicely formatted HTML representation of the model, which is made possible by implemention of these special methods.

This special method _repr_*_ are called by Jupyter notebook to render the object in different formats, enhancing the user experience when working with complex objects.

from sklearn.linear_model import LogisticRegression
model = LogisticRegression()
model  # In a Jupyter notebook, this will display a rich HTML representation of the model

The output will be a nicely formatted HTML representation of the Logistic Regression model, showing its parameters and other relevant information in a user-friendly way.

👉 In the next part, we’ll explore the different representation methods that support Jupyter notebooks (such as _repr_html_, _repr_mimebundle_, and others) and learn when and how to use them.

Next Part: https://wearexplorer.com/2025/10/21/mastering-jupyters-special-repr-methods/

Reference Links:

1. https://discuss.python.org/t/what-are-the-differences-between-str-and-repr-in-class-methods/44142
2. https://docs.python.org/3/reference/datamodel.html#object.repr

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