Python etc / __new__ and __init__

Published: 15 October 2020, 18:00

Creation of class instance is done by __call__ method of object class (provided by metaclass type) and practically includes only 2 steps:

  1. Call the __new__ method to create an instance.
  2. Call the __init__ method to set up the instance.
class A:
  def __new__(cls, *args):
    print('new', args)
    return super().__new__(cls)

  def __init__(self, *args):
    print('init', args)

# new (1,)
# init (1,)

# new (1,)
# init (1,)

So, if you want to create an instance without executing __init__, just call __new__:

A.__new__(A, 1)
# new (1,)

Of course, that’s a bad practice. The good solution is to avoid a heavy logic in __init__ so nobody wants to avoid calling it.