What is the difference between str and repr in Python? The __str__ and __repr__ methods are two commonly used "dunder" (double underscore) methods that can be used to define how an object is represented as a string.
Both methods, str and repr, generate a string representation of an object, but they serve different purposes and people use them in different contexts.
In this article, we will explore the differences between __str__ and __repr__, when to use each method, and provide examples of how to implement them in your Python code.
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1. Examples of str() and repr()
Before getting into the details of __str__ and __repr__ , let's see where it can be useful. The str() function returns a string representation of the object that is meant to be human-readable
The repr() function, on the other hand, returns a string representation of the object that is meant to be unambiguous and complete.
my_list = [1, 2, 3]
print(str(my_list))
# '[1, 2, 3]'
print(repr(my_list))
# '[1, 2, 3]'
In the example above you have seen how these two methods, give the same output. But there are some differences between these two, which we will see in the upcoming section.
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2. What is str in Python?
The __str__ method is a special method in Python that defines a human-readable string representation of an object. It is called automatically when the object is printed or passed to the str() function.
The purpose of the __str__ method is to provide a concise and easy-to-understand string representation of the object, intended for humans rather than machines.
See the following Example of using the __str__ method:
class ProgrammingLanguage:
def __init__(self, name, year, designed_by):
self.name = name
self.designed_by = designed_by
def __str__(self):
return f"{self.name} by {self.designed_by}"
object= ProgrammingLanguage("Python", "Guido van Rossum")
print(python)
# Output: "Python by Guido van Rossum"
In the above example the __str__ method is used to convert a Python Object to a string representation. We have overridden the __str__ method.
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3. What is repr in Python?
The __repr__ is also used to define a string representation of an object, typically for debugging or logging purposes. This method is called "repr" which stands for "representation". It returns a string representation of an object that can be used to recreate the object.
The __repr__ method is called when the repr() function is used on an object or when the object is printed in the Python REPL. The string returned by the __repr__ method should be a valid Python expression that, when evaluated, would create an object identical to the original object.
class ProgrammingLanguage:
def __init__(self, name, year, designed_by):
self.name = name
self.designed_by = designed_by
def __repr__(self):
return f"ProgrammingLanguage('{self.name}' ,'{self.designed_by}')"
python = ProgrammingLanguage("Python","Guido van Rossum")
print(repr(python))
# Output: "ProgrammingLanguage('Python', 'Guido van Rossum')"
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4. Difference Between str and **repr**
Both the __str__ and __repr__ methods in Python are used to define string representations of objects, but they serve slightly different purposes.
__str__is for making objects readable to humans, while__repr__is for making objects unambiguous to the computer.__str__is used when you want to display an object to a user, while__repr__is used when you want to display an object to the computer, such as when debugging.__str__can return a simplified representation of the object, while__repr__should return a complete representation that can be used to recreate the object.
The following Table summarizes the differences between __str__ and __repr__ in Python:
| | str | repr |
| --- | --- | --- |
| Purpose | Human-readable | Formal and unambiguous |
| When called | str() function | repr() function, object printed in REPL |
| String representation | Readable but incomplete | Complete and valid Python expression |
| Format | Should be easy to read by humans | Does not need to be easy to read by humans |
| Example | "ProgrammingLanguage(name='Python')" | main.ProgrammingLanguage object at 0x… |
| Usage | Used for user-friendly display of an object | Used for debugging, logging, and re-creating an object |
| Returns | A string representing the object's state or values | A string that, when evaluated, can be used to re-create the object |
| Customization | Can be customized to improve object representation | Can be customized to improve object representation or debugging output |
| Fallback | If __str__ is not defined, uses __repr__ | If __repr__ is not defined, uses a default representation of the object |
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5. Examples of str and repr
Some examples of when you might want to use str:
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5.1 Example 1
A class that represents a user profile, you might want to define __str__ and __repr__ to return the user's name, email, and a short bio.
class UserProfile:
def __init__(self, name, email, bio):
self.name = name
self.email = email
self.bio = bio
def __str__(self):
return f"{self.name} ({self.email}): {self.bio}"
def __repr__(self):
return f"UserProfile(name={self.name}, email={self.email}, bio={self.bio})"
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5.2 Example 2
If you have a class that represents a book, you might want to define __str__ and __repr__ to return the book's title, author, and publication date.
class Book:
def __init__(self, title, author, publication_date):
self.title = title
self.author = author
self.publication_date = publication_date
def __str__(self):
return f"\"{self.title}\" by {self.author} ({self.publication_date})"
def __repr__(self):
return f"Book(title={self.title}, author={self.author}, publication_date={self.publication_date})"
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5.3 Example 3
If you have a class that represents a product, you might want to define __str__ and __repr__ to return the product's name, price, and description.
class Product:
def __init__(self, name, price, description):
self.name = name
self.price = price
self.description = description
def __str__(self):
return f"{self.name}: ${self.price} - {self.description}"
def __repr__(self):
return f"Product(name={self.name}, price={self.price}, description={self.description})"
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6. Summary and Conclusion
In conclusion, the difference between str and repr is an important concept in Python to understand. You use str to define a human-readable string representation of an object, and you use repr to define a formal and unambiguous string representation of an object.
Remember, str is for human-readable string representations, while repr is for unambiguous and machine-readable string representations. If you have any questions leave them in the comment section.
Happy coding!
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