Automatically calling class function after init

Question

I want to automate a class method which would be called right after __init__ has completed.

e.g,

class A:
    def __init__(self):
        initialization statement
    def post_init(self):
        #this should be automatically called after completion of __init__ function.
        some statement

How can I achieve this?

Answer 1

If you want to run post_init automatically after __init__ for this class and all inheriting classes you need to mess with how objects are instantiated using metaclasses. By default when you __call__ a class using A() it invokes a __new__ to create a new object and then an __init__ method of that object. You want to add the post_init to that sequence

class MyMetaclass(type):
  def __call__(cls, *args, **kwargs):
    new_obj = type.__call__(cls, *args, **kwargs)
    new_obj.post_init()
    return new_obj

class A(metaclass=MyMetaclass):
  def __init__(self):
    print('init called')

  def post_init(self):
    print('post init called')

You can verify that

>>> A()
init called
post init called
<__main__A at 0x7f3988e2c6a0>