__new__

As explained in Python Workout, Second Edition

__new__ is a Python special method that creates and returns a new instance before initialization occurs.

__new__ creates and returns a new instance before __init__ runs. Calling Foo(10) invokes __new__, which creates the object, triggers __init__, and returns the initialized instance. __init__ adds attributes; it does not create the object. Custom __new__ implementations are rarely necessary. section 10.8

Trace a simple instance

With class Foo defining __init__(self, x) and assigning self.x = x, calling f = Foo(10) creates the instance through __new__, initializes x through __init__, and makes f.x available. section 10.8

When we create an object, __new__ is invoked.

Use the sequence diagrams to distinguish instance creation by __new__ from initialization by __init__ and final return to the caller. section 10.8

How Python Workout, Second Edition covers it

How deep it goes

Traces creation, initialization, and return, while deferring custom __new__ implementation as rarely necessary.

Examples

Uses Foo(10), self.x, and f.x to demonstrate creation followed by attribute initialization.

What you can do after

Understand the execution order behind class calls and avoid mistaking __init__ for the instance-creation method.

How it connects

Connects __new__ with classes, __init__, instances, attributes, and callable class invocation.

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Also explained in

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  liveBookmanning.com
  Python How-To__new__ is Python's special class-level method that creates and returns a new instance before initialization.
• 

  liveBookmanning.com
  Python Workout: 50 ten-minute exercisesA Python special method responsible for creating and returning a new instance before initialization occurs.

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Related concepts

• objectproduces · A computational object is a runtime entity or structured value representing data, state, or a resource, with properties or operations defined by its programming model.
• initializerused by · An initializer is a function, declaration, or language construct that establishes the initial value or state of an object, value, computation, or process.
• constructor methodcontrasts with · A constructor is a type-associated operation or callable that creates or initializes an instance and establishes its initial state.
• Singleton patternused by · The Singleton pattern restricts a type or component to one shared instance within a defined scope and provides a way to access it.

This explainer was generated by Manning's knowledge graph from the text of Python Workout, Second Edition. The section links point to the parts of the book it draws on.