String representation methods in Python - Step-by-Step Execution

Concept Flow - String representation methods

Create object

↓

Call str(obj)

↓

__str__ method runs

↓

Return user-friendly string

↓

Call repr(obj)

↓

__repr__ method runs

↓

Return developer-friendly string

When you print or convert an object to string, Python calls __str__ for user-friendly text and __repr__ for developer-friendly text.

Execution Sample

Python

class Cat:
    def __str__(self):
        return "A cute cat"
    def __repr__(self):
        return "Cat()"

c = Cat()
print(str(c))
print(repr(c))

This code shows how __str__ and __repr__ methods return different strings for the same object.

Execution Table

Step	Action	Method Called	Returned String	Output
1	Create Cat object c	N/A	N/A	No output
2	Call str(c)	__str__	"A cute cat"	A cute cat printed
3	Call repr(c)	__repr__	"Cat()"	Cat() printed

💡 All string representation methods executed, program ends

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
c	undefined	Cat object	Cat object	Cat object

Key Moments - 2 Insights

Why does print(str(c)) show a different string than print(repr(c))?

Because str(c) calls __str__ which returns a user-friendly string, while repr(c) calls __repr__ which returns a developer-friendly string, as shown in steps 2 and 3 of the execution_table.

What happens if __str__ is not defined but __repr__ is?

Python uses __repr__ as a fallback for str(), so print(str(obj)) will show __repr__ output. This is implied by the flow where __str__ is called first, but if missing, __repr__ is used.

Visual Quiz - 3 Questions

Look at the execution_table, what string does __str__ return at step 2?

A "<Cat object>"

B "Cat()"

C "A cute cat"

D "None"

💡 Hint

Check the 'Returned String' column at step 2 in execution_table

At which step is the developer-friendly string returned?

A Step 1

B Step 3

C Step 2

D No step returns it

💡 Hint

Look at the 'Method Called' column to find __repr__ call in execution_table

If __str__ method was removed, what would print(str(c)) output?

A "Cat()"

B Error

C "A cute cat"

D "None"

💡 Hint

Recall key_moments explanation about __repr__ fallback when __str__ is missing

Concept Snapshot

String representation methods:
- __str__ returns user-friendly string for print()
- __repr__ returns developer-friendly string for debugging
- print(obj) calls __str__ if exists, else __repr__
- Use __repr__ to show unambiguous info
- Use __str__ for readable output

Full Transcript

This lesson shows how Python uses two special methods to convert objects to strings: __str__ and __repr__. When you print an object or use str(), Python calls __str__ to get a user-friendly string. When you use repr(), Python calls __repr__ to get a developer-friendly string. In the example, the Cat class defines both methods. Creating a Cat object and printing str(c) shows 'A cute cat', while repr(c) shows 'Cat()'. If __str__ is missing, Python uses __repr__ as a fallback. This helps you control how your objects appear in printouts and debugging.