Python

Magic OR Dunder method in Python

• These methods provide flexibility use python built-in function with custom object
• Here is few magic methods, -

Python Built-In Function	Class level method declaration	Description
print{instance}	_ _str__(self)	This method return instance string representations.
len{instance}	_ _len__(self)	This method return length attribute of instance.
del instance	_ _del__(self)	This method delete instance from memory.

• Example. -

  #class to store book information.
  class BookInformation():
      def __init__(self, bookName, bookAuthor, bookPages):
          self.bookName = bookName
          self.bookAuthor = bookAuthor
          self.bookPages = bookPages
          print('BookInformation instance created.')
     
      def __str__(self):
          return f'Name - {self.bookName} Author - {self.bookAuthor} Pages - {self.bookPages}'
         
      def __len__(self):
          return self.bookPages
         
      def __del__(self):
          print(f'Deleting book information of name - {self.bookName}')
  

  #Creating an custom instance of BookInformation class
  book = BookInformation('Java Book','Bhushan Patil', 300)
  

  Output =>

  BookInformation instance created.
  

  #Printing book instance
  print(book)
  

  Output =>

  Name - Java Book Author - Bhushan Patil Pages - 300
  

  #Checking length of book.pages attribute.
  len(book)
  

  Output =>

  300
  

  #Deleting book instance from memory.
  del book
  

  Output =>

  Deleting book information of name - Java Book
  

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