Is it reasonable to let init member must take self parameter?

Question

I find when __init__ method lacks self parameter, only if there is no instantiation of this class, the compiler won't complain:

$ cat test.py
#!/usr/bin/python
class A():
    def __init__():
        print("A()")
$ ./test.py

But if there is a instantiation, the running time error will occur:

$ cat test.py
#!/usr/bin/python
class A():
    def __init__():
        print("A()")

A()
$ ./test.py
Traceback (most recent call last):
  File "./test.py", line 6, in <module>
    A()
TypeError: __init__() takes 0 positional arguments but 1 was given

Per my understanding, __init__() seems no use because it can't make any instance. So why doesn't the Python compiler enforce limitation such as when no self parameter in __init__ function, it will show error message? Is it reasonable? Or I miss something.

You should modify the declaration of init from `def __init__():` to: `def __init__(self):` any class method should have `self` passed in as the first argument. — Nir Alfasi, Aug 29 '17 at 02:48
The thing is, it's not an error when you don't include the self argument. The `__init__` just doesn't take an argument. BUT when you create an instance, Python implicitly calls the initializer WITH A PARAMETER, the instance. Thus the error. — Andrew Li, Aug 29 '17 at 02:52
Why add more special cases? The closer `__init__` is to every other method, the better. Python will let you write `{**5}` and other things that don’t usually make sense, too, as long as you don’t run them. — Ry-, Aug 29 '17 at 02:53

score 0 · Answer 1 · answered Aug 29 '17 at 02:56

__init__ is not a special name at compilation time.

It is possible to do things with the symbol A.__init__ other than invoke it by trying to construct an A, and I think it is possible to replace the unusable __init__ function with a different function at runtime prior to trying to construct an A.

The check for a correct number of arguments is made when __init__ is called, as it is for any other method.

score 0 · Answer 2 · answered Aug 29 '17 at 03:07

0

it must be one argument at least, we call it "self" usually, so your Python code maybe have a small change

#!/usr/bin/python
class A(object):
    def __init__(self):
        print("A()")

A()

answered Aug 29 '17 at 03:07

mayor

11
2

score 0 · Answer 3 · answered Aug 29 '17 at 03:17

__init__ is the initialization of an already created instance of a class, therefore it needs self, just like every other class method. If you want to handle the creation of the class, that is the __new__ method. This seems like a good description.

Don't let the fact that python doesn't complain unless the method is called confuse you.

Is it reasonable to let __init__ member must take self parameter?

3 Answers3

Is it reasonable to let init member must take self parameter?