Re: super().__init__() and bytes

Op 3/12/2024 om 10:41 schreef Roel Schroeven via Python-list:

[...]
When I try the same with bytes as base class though, that doesn't work (at least in the Python version I'm using, which is CPython 3.11.2 64-bit on Windows 10):
>
class MyBytes(bytes):
    def __init__(self, data):
        super().__init__(data)
print(MyBytes(b'abcdefghijlkmn'))
>
This results in an exception:
>
Traceback (most recent call last):
  File "test_mybytes.py", line 4, in <module>
    print(MyBytes(b'abcdefghijlkmn'))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "test_mybytes.py", line 3, in __init__
    super().__init__(data)
TypeError: object.__init__() takes exactly one argument (the instance to initialize)
>
I'm passing two arguments (data and the implicit self), and apparently that's one too many. Let's try without arguments (i.e. only the implicit self):
>
class MyBytes(bytes):
    def __init__(self, data):
        super().__init__()
print(MyBytes(b'abcdefghijlkmn'))
>
Now it works, and prints b'abcdefghijlkmn'. The same happens with int as base class, and presumably a number of other classes.

As a follow-up, it looks like this behavior is because bytes and int are immutable. When I try with bytesarray instead of bytes, which works largely the same but is mutable, things do work as I expect. There's a hint in the documentation of __new__(): "__new__() is intended mainly to allow subclasses of immutable types (like int, str, or tuple) to customize instance creation". But that doesn't tell me why using super().__init__(<custom arguments>) doesn't work for immutable classes.
The documentation for __init__() says " If a base class has an __init__() method, the derived class’s __init__() method, if any, must explicitly call it to ensure proper initialization of the base class part of the instance; for example: super().__init__([args...])". So does that mean that bytes and int not have an __init__() method? Is there a link between being immutable and not having __init__()?
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