Python __new__, __init__ and __del__ example script

py_new_init.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from __future__ import print_function

class Foo(object):
  def __new__(cls, *args, **kwargs):
    print("Foo.__new__ invoked")
    print("args:", args)
    print("kwargs:", kwargs)
    # in python3, you can just simply call super() here
    super_obj = super(Foo, cls)
    if super_obj.__new__ is object.__new__:
      # reach the end of class mro (object)
      self = super_obj.__new__(cls)
    else:
      self = super_obj.__new__(cls, *args, **kwargs)
    # the use of super() here seems to be irrelevent,
    # but super() really comes to handy when we're dealing
    # with inheritance

    return self

  def __init__(self, *args, **kwargs):
    # Note that __init__ must share the same API as __new__
    # since all the arguments for __new__ will be passed to __init__
    # according to the python website (https://docs.python.org/3.6/reference/datamodel.html#object.__new__)
    print("Foo.__init__ invoked")
    self.args = args
    for k, v in kwargs.items():
      setattr(self, k, v)

  def __del__(self):
    print("Foo.__del__")
    super_obj = super(Foo, self)
    try:
        super_obj.__del__()
    except:
        # object do not have __del__ method
        pass

class Bar(Foo):
  def __del__(self):
      print("Bar.__del__")
      super_obj = super(Bar, self)
      super_obj.__del__()

if __name__ == "__main__":
  b = Bar(1, 2, a=3, b=2)
  b = 3