Why is __init__() always called after __new__() in Python?

by

Use __new__ when you need to control
the creation of a new instance.

Use
__init__ when you need to control initialization of a new instance.

__new__ is the first step of instance creation. It’s called first, and is
responsible for returning a new
instance of your class.

In contrast,
__init__ doesn’t return anything; it’s only responsible for initializing the
instance after it’s been created.

In general, you shouldn’t need to
override __new__ unless you’re
subclassing an immutable type like
str, int, unicode or tuple.

From April 2008 post: When to use __new__ vs. __init__? on mail.python.org.

You should consider that what you are trying to do is usually done with a Factory and that’s the best way to do it. Using __new__ is not a good clean solution so please consider the usage of a factory. Here’s a good example: ActiveState Fᴀᴄᴛᴏʀʏ ᴘᴀᴛᴛᴇʀɴ Recipe.

More Related Contents:

  1. Why is __init__() always called after __new__()?
  2. Using a class’ __new__ method as a Factory: __init__ gets called twice
  3. How to sum all range output in python 3
  4. Python for in range()
  5. __init__() missing 1 required positional argument ‘address’
  6. How to solve “error: Microsoft Visual C++ 14.0 or greater is required” when installing Python packages?
  7. How to specify multiple return types using type-hints
  8. Are lists thread-safe?
  9. Relative imports in Python 3
  10. What are type hints in Python 3.5?
  11. How can I change a global variable from within a function?
  12. Size of list in memory
  13. Python 3: EOF when reading a line (Sublime Text 2 is angry)
  14. Is there a way to set a default parameter equal to another parameter value?
  15. Why is exponentiation applied right to left?
  16. How can I generate a list of consecutive numbers?
  17. PyEval_InitThreads in Python 3: How/when to call it? (the saga continues ad nauseam)
  18. Prevent creating new attributes outside __init__
  19. Logging to two files with different settings
  20. “RuntimeError: generator raised StopIteration” every time I try to run app
  21. Why do numbers in a string become “x0n” when a backslash precedes them?
  22. How to call an async function without await?
  23. “Permission Denied” trying to run Python on Windows 10
  24. Using asyncio.Queue for producer-consumer flow
  25. Are there any reasons not to use an OrderedDict?
  26. Changing one dict changes all dicts in a list of dicts [duplicate]
  27. List comprehension scope error from Python debugger
  28. Error: No module named ‘fcntl’
  29. Multiple lines of x tick labels in matplotlib
  30. Namespace vs regular package

Leave a Comment