Understanding __repr__ in Python Classes

[Rajeev Bagra]

When learning Python classes, one special method you will often encounter is:

__repr__()

At first glance, it may look strange because of the double underscores, but it plays a very important role in making objects readable and easier to debug.

---

The Example Class

Consider the following class:

class RunningEvent:
    """ The class models a foot race event of a length of n metres """

    def __init__(self, length: int, name: str = "no name"):
        self.length = length
        self.name = name

    def __repr__(self):
        return f"{self.length} m. ({self.name})"

This class models a running race event.

• length stores the race distance
• name stores the race name
• __repr__ defines how the object should appear when displayed

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What Happens Without __repr__?

Suppose we create an object:

race = RunningEvent(100, "Sprint")
print(race)

If the class did not define __repr__, Python would display something like:

<__main__.RunningEvent object at 0x7f2b1c4>

This output represents:

• the class name
• the memory address of the object

While useful internally, it is not very human-friendly.

---

What __repr__ Does

Now look at this method again:

def __repr__(self):
    return f"{self.length} m. ({self.name})"

This tells Python:

“Whenever this object is displayed, show it in this format.”

So:

race = RunningEvent(100, "Sprint")
print(race)

produces:

100 m. (Sprint)

This is much easier to understand.

---

Understanding the f-string

The line:

f"{self.length} m. ({self.name})"

is called an f-string.

It inserts object attributes into a string.

If:

self.length = 200
self.name = "Quarter Mile"

then the returned string becomes:

"200 m. (Quarter Mile)"

---

Why __repr__ is Useful

The __repr__ method helps in:

• debugging programs
• printing objects clearly
• displaying lists of objects
• making classes more readable

For example:

events = [
    RunningEvent(100),
    RunningEvent(200, "Final")
]

print(events)

Output:

[100 m. (no name), 200 m. (Final)]

Without __repr__, the list would display confusing memory addresses instead.

---

Plain English Analogy

Think of __repr__ as an object’s self-introduction.

Without __repr__:

“Hi, I am object #0x7fa21…”

With __repr__:

“Hi, I am a 100 metre race called Sprint.”

---

Key Takeaway

The __repr__ method allows developers to control how objects appear when printed or inspected.

It makes programs easier to understand and is especially valuable when working with:

• custom classes
• debugging
• lists of objects
• data models

Whenever you create your own Python classes, adding a meaningful __repr__ method is considered a good programming practice.

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