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Practice

Special Methods in Classes

In Python, Special Methods are predefined methods within a class that define the behavior of objects and assist in interaction with Python's built-in functions.

These methods are also called Magic Methods, starting and ending with double underscores (__).

For example, you can represent an object as a string using (__str__) or compare two objects using (__eq__).


Examples of Using Special Methods​

The code example below defines a Book class using the __str__ and __eq__ special methods.

The __str__ method is a special method that defines the string representation of an object, called when converting an object to a string using the print function or the str function.

Generally, the __str__ method is used to present the object's information in a human-readable format.

The __eq__ method is a special method that defines equality comparison between objects, executed when the == operator is used to compare two objects.

__str__, __eq__ Special Methods Example
# Define class Book
class Book:
    # Initialization method
    def __init__(self, title, author):
        self.title = title  # Book title
        self.author = author  # Author name

    # __str__ method: Converts the object into a human-readable string
    def __str__(self):
        return f"{self.title} by {self.author}"  # Return with string formatting

    # __eq__ method: Compares two objects based on title and author
    def __eq__(self, other):
        # Returns True if titles and authors are equal, otherwise False
        return self.title == other.title and self.author == other.author
print(book1 == book3)   # False

In this example, the __str__ method converts the object into a human-readable string, and the __eq__ method compares whether the title and author of two objects are the same.

The Book class can be used as follows:

Example of Creating and Using Book Objects
# Create Book objects
book1 = Book("Harry Potter", "J.K. Rowling")
book2 = Book("Harry Potter", "J.K. Rowling")
book3 = Book("The Lord of the Rings", "J.R.R. Tolkien")

# __str__ method example: Outputs in a human-readable format when printing
print(book1)
# Outputs "Harry Potter by J.K. Rowling"

# __eq__ method example: Compare objects
print(book1 == book2)
# True, both objects have the same title and author
print(book1 == book3)
# False, different title and author

# Manage Book objects in a list
book_list = [book1, book2, book3]

# Output book information in the list (applies __str__ method to all objects)
for book in book_list:
    print(book)

# Result:
# Harry Potter by J.K. Rowling
# Harry Potter by J.K. Rowling
# The Lord of the Rings by J.R.R. Tolkien

In the code above, book1, book2, and book3 are instances of the Book class.

By defining the __str__ method, you can output the object in a human-readable format when using print(book1).

By defining the __eq__ method, you can compare whether title and author are the same when using book1 == book2.


What are Some Special Methods?​

  • __str__(self): Used to provide a string representation of an object. It's called by the print() function or the str() function.

  • __eq__(self, other): Overrides the == operator to define equality comparison between objects.

  • __ne__(self, other): Overrides the != operator to compare differences between objects.

  • __gt__(self, other): Overrides the > operator to define size comparison between objects.

  • __ge__(self, other): Overrides the >= operator to define size comparison between objects.

  • __lt__(self, other): Overrides the < operator to define size comparison between objects.

  • __le__(self, other): Overrides the <= operator to define size comparison between objects.

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