Why doc call `__init__` as a method rather than function?

[Cameron Simpson]

On 15Sep2023 10:49, scruel tao <scruelt at hotmail.com> wrote:
>```python
>>>> class A:
>...   def __init__(self):
>...     pass
>...
>```
>
>On many books and even the official documents, it seems that many authors prefer to call `__init__` as a "method" rather than a "function".
>The book PYTHON CRASH COURSE  mentioned that "A function that’s part of a class is a method.", however, ` A.__init__` tells that `__init__` is a function...

As mentioned, methods in Python _are_ functions for use with a class.

>>>> A.__init__
><function A.__init__ at 0x0000026CFC5CCEE0>
>>>> a = A()
>>>> a.__init__
>
><bound method A.__init__ of <__main__.A object at 0x0000026CFC1BB400>>
>I wonder how can I call `__init__` as? Consider the output above.
>Maybe both are OK?

As you can see, they're both legal expressions.

The thing about `__init__` is that it's usually called automatically 
which you make a new object. Try putting a `print()` call in your 
`__init__` method, then make a new instance of `A`.

The purpose of `__init__` is to initialise the object's attribute/state 
after the basic, empty-ish, object is made.

Like other dunder methods (methods named with double underscores front 
and back) it is called automatically for you. In a subclass the 
`__init__` method calls the subperclass `__init__` and then does 
whatever additional things might be wanted by the subclass.

Let's look at what you used above:

     >>> A.__init__
     <function A.__init__ at 0x0000026CFC5CCEE0>

Here's we've just got a reference to the function you supposlied with 
the class definition for class `A`.

This:

     >>> a = A()
     >>> a.__init__
     <bound method A.__init__ of <__main__.A object at 0x0000026CFC1BB400>

Here's you've accessed the name `__init__` via an existing instance of 
`A`, your variable `a`. At this point you haven't called it. So you've 
got a callable thing which is a binding of the function to the object 
`a` i.e. when you call it, the "bound method" knows that t is associated 
with `a` and puts that in as the first argument (usually named `self`).

Cheers,
Cameron Simpson <cs at cskk.id.au>