The following code causes an assertion failure:
    import _struct
    struct_obj = _struct.Struct.__new__(_struct.Struct)
    struct_obj.iter_unpack(b'foo')

This is because Struct_iter_unpack() (in Modules/_struct.c) assumes that
Struct.__init__() was called, and so it does `assert(self->s_codes != NULL);`.

The same happens in (almost) every method of Struct, and in s_get_format(), so
in all them, too, we would get an assertion failure in case of an uninitialized
Struct object.
The exception is __sizeof__(), which doesn't have an `assert`, and simply
crashes while trying to iterate over `self->s_codes`.


I would open a PR to fix this soon.

What are the drawbacks of moving all code from __init__ to __new__, at least in master branch (3.8)? IMO it's much more robust than playing whack-a-mole both with ref/memleaks caused by repeated calls to __init__ and absence of initialization checks in all methods.

Reproduced on 3.11.

messages: + msg404285
versions: + Python 3.9, Python 3.10, Python 3.11, - Python 2.7, Python 3.7, Python 3.8

messages: + msg325462
versions: + Python 2.7, Python 3.6, Python 3.8