What is the difference between __str__ and __repr__ in Python?

The __str__ and __repr__ methods in Python serve different purposes for string representation of objects. The __str__ method provides a human-readable representation, while __repr__ provides an unambiguous, developer-friendly representation that ideally can recreate the object.

Key Differences

The built-in functions str() and repr() call the __str__() and __repr__() methods respectively. The repr() function computes the official representation of an object, while str() returns the informal representation.

Example with Integer Objects

For simple objects like integers, both methods return the same result ?

x = 1 
print("repr(x):", repr(x))
print("str(x):", str(x))

repr(x): 1
str(x): 1

Example with String Objects

For string objects, the difference becomes clear ?

x = "Hello"
print("repr(x):", repr(x))
print("str(x):", str(x))

repr(x): 'Hello'
str(x): Hello

Evaluating with eval()

The repr() result can be evaluated with eval() to recreate the object, while str() cannot ?

x = "Hello"
y1 = repr(x)
print("repr result:", y1)
print("eval(repr):", eval(y1))

y2 = str(x)
print("str result:", y2)

# This would cause NameError
try:
    eval(y2)
except NameError as e:
    print("eval(str) error:", e)

repr result: 'Hello'
eval(repr): Hello
str result: Hello
eval(str) error: name 'Hello' is not defined

Custom Class Example

Here's how to implement both methods in a custom class ?

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def __str__(self):
        return f"{self.name}, {self.age} years old"
    
    def __repr__(self):
        return f"Person('{self.name}', {self.age})"

person = Person("Alice", 30)
print("str():", str(person))
print("repr():", repr(person))

str(): Alice, 30 years old
repr(): Person('Alice', 30)

Conclusion

Use __repr__ for unambiguous, developer-friendly output that can ideally recreate the object. Use __str__ for readable, user-friendly display. When only one is defined, Python uses __repr__ as a fallback for str().