String Representation: __str__ vs. __repr__

In Python, every object has a string representation. By default, custom objects look like a cryptic memory address: <__main__.Car object at 0x7f...>. To make your objects professional and easy to debug, you must override the “Magic Methods” responsible for string output.

The Python Data Model provides two distinct methods for this: __str__ and __repr__.

---

1. __str__: The “User” View

The __str__ method is meant to be informal and readable. Its primary goal is to provide a clear summary for an end-user.

• Triggered by: print(obj), str(obj), and f-strings {obj}.
• Goal: To be pretty.

str_demo.py

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author

    def __str__(self):
        return f"'{self.title}' by {self.author}"

my_book = Book("1984", "George Orwell")
print(my_book) # Output: '1984' by George Orwell

---

2. __repr__: The “Developer” View

The __repr__ (Representation) method is meant to be unambiguous and formal. Its primary goal is to provide enough information to recreate the object.

• Triggered by: The interactive console, repr(obj), and inside collections (like lists).
• Goal: To be precise.

repr_demo.py

class Book:
    # ... __init__ ...

    def __repr__(self):
        return f"Book(title='{self.title}', author='{self.author}')"

# In a list, Python uses __repr__
library = [Book("1984", "Orwell"), Book("Dune", "Herbert")]
print(library)
# Output: [Book(title='1984', author='Orwell'), Book(title='Dune', author='Herbert')]

The Golden Rule of __repr__

Whenever possible, the output of __repr__ should look like a valid Python command that would create a new instance of that class.

---

3. The Fallback Mechanism

What happens if you only define one of them?

• If you define only __repr__: Python uses it for both print() and the console.
• If you define only __str__: Python uses it for print(), but the console/lists will still show the ugly <__main__...> address.

Best Practice: Always define __repr__ first. It’s the “fallback” that ensures your objects are always debuggable.

---

4. Under the Hood: Evaluation vs. Display

The distinction between these two comes from the philosophy that an object has an Identity (how the computer sees it) and a Value (how the human sees it).

• __repr__ answers: “What is this object?”
• __str__ answers: “What information does this object hold?”

When you use the REPL, Python calls repr() on every result to show you the “Raw” object. When you use print(), Python calls str() to give you a “Pretty” version.

---

5. Summary Table

Feature	__str__	__repr__
Intended Audience	End User	Developer / Debugger
Output Style	Informal / Pretty	Formal / Unambiguous
Default Fallback	object.__repr__	object.__repr__
Best Practice	Optional.	Highly Recommended.