super().__init__() and bytes

[Anders Munch]

Roel Schroeven <roel at roelschroeven.net> wrote:
> As a follow-up, it looks like this behavior is because bytes and int are immutable.

Yes.

> But that doesn't tell me why using super().__init__(<custom arguments>) doesn't work for immutable classes.

bytes.__init__ does work, but it's just an inherited object.__init__, which does nothing, and takes no parameters.
 __init__ cannot change the value of the bytes object; the value is set by bytes.__new__ and cannot change after that.

Best not to define an __init__ method at all, just use __new__.

Something like:

class BytesSubclass(bytes):
    def __new__(cls, whatever, arguments, you, like):
        bytesvalue = compute(whatever, arguments, you, like)
        ob = bytes.__new__(cls, bytesvalue)
        ob.some_other_att = compute_something_else(whatever, arguments, you, like)
        return ob

regards, 
Anders