__new__ in Python

Python, a versatile and broadly used programming language, is thought for its simplicity and widespread feature set. One of its lesser-regarded but powerful capabilities is the brand-new technique, which offers builders a unique way of customizing item introduction. This article presents a complete and engaging review of the new approach in Python, discussing its purpose, use instances and quality practices.

Section 1: The Essence of New

1.1: Understanding New

In Python, new is a special method that belongs to elegance rather than the example of a category. It is chargeable for creating and returning new times of the class. The new method is called before the init method and is usually applied when you want to control the item advent method or the allocation of assets.

1.2: The Purpose of New

The primary purpose of new is to offer greater control over object instantiation, allowing developers to customize object creation, manage the allocation of resources, and even implement singleton design patterns. While not commonly used, new can be a powerful tool when applied correctly.

Section 2: A Basic Example of New

To reveal the utilization of recent, let's have a look at a simple instance. Suppose we have a class known as "Person" and we need to make certain that only instances with non-empty names are created.

  • Define the Person class with a __new__ method.

  • Check if the 'call' argument isn't always empty.

  • Raise a ValueError if the name is empty.

  • Call the superclass's __new__ approach to create and return a new instance if the name is valid.

  • Define the __init__ technique to set the 'name' attribute.

class Person:
   def __new__(cls, name):
      if not name:
         raise ValueError("Name cannot be empty.")
      return super().__new__(cls)
   def __init__(self, name):
      self.name = name

   john = Person("John")
   print(john.name)  # Output: John
   empty_person = Person("")
except ValueError as e:


Name cannot be empty.

In this example, we create a "Person" class that only allows instances with non-empty names.

Section 3: Advanced Use Cases

3.1: Implementing the Singleton Design Pattern

One practical use case of the new method is to implement the Singleton design pattern, ensuring that only one instance of a class can be created.

  • Define the Singleton class with a class attribute _instance set to None.

  • Implement the __new__ method in the Singleton class.

  • Check if _instance is None.

  • On the off chance that _instance is None, make a new instance utilizing the superclass's __new__ method and allot it to _instance.

  • Return the existing _instance.

class Singleton:
   _instance = None
   def __new__(cls, *args, **kwargs):
      if cls._instance is None:
         cls._instance = super().__new__(cls)
      return cls._instance

singleton1 = Singleton()
singleton2 = Singleton()

print(singleton1 is singleton2) 



If _instance is None, create a new instance of the usage of the superclass's __new__ method and assign it to _instance.

3.2: Customizing Object Creation for Immutable Classes

Another use case for the new method is customizing object introduction for immutable classes. Let’s have a look at the below example for using a custom string class −

  • Define the CustomString class that inherits from the str class.

  • Implement the __new__ method in the CustomString class.

  • Validate if the provided value is an instance of str.

  • Convert it to a string, If the value is not an instance of str.

  • Call the superclass's __new__ method with the uppercase model of the string to create and return a new instance.

class CustomString(str):
   def __new__(cls, value):
      if not isinstance(value, str):
         value = str(value)
      return super().__new__(cls, value.upper())

custom_string = CustomString("hello world")



In this example, we create a CustomString class that inherits from the built-in str class and customizes the object creation process:

Section 4: Best Practices for Using __new__

4.1: Always Call the Superclass's __new__ Method

When enforcing the __new__ method, it's important to call the superclass's __new__ method using `splendid().__new__(cls, *args, **kwargs)`. This guarantees that the object introduction procedure follows the best inheritance chain and that any required sources are allotted.

4.2: Use __new__ Sparingly

Since __new__ is a powerful yet potentially confusing feature, it should be used judiciously and only when necessary. In most cases, the default object creation process provided by Python is sufficient. Use __new__ only when you need precise control over the instantiation process, such as in Singleton patterns or when working with immutable classes.

4.3: Recognize the Difference Between __new__ and __init__

Remember that __new__ is responsible for creating and returning a new instance, even as __init__ initializes the example. Both methods have exceptional functions and should no longer be used interchangeably. Typically, __new__ is used while you want to govern the creation manner, at the same time as __init__ is used for initializing instance attributes.


The __new__ method in Python is an effective yet lesser-known function that permits developers to customize item introduction and manipulate the allocation of sources. By knowing its purpose, using instances, and first-rate practices, developers can harness the overall capacity of __new__ and improve the flexibility and efficiency of their Python programs.

Updated on: 09-May-2023


Kickstart Your Career

Get certified by completing the course

Get Started