Python increment function

increment-example.py

import ctypes

_bases = (ctypes.Structure,)
PyLongPointer = ctypes.POINTER(
    type("PyLong", _bases, dict(_fields_=[
        ("ob_base", type("PyVarObject", _bases, dict(_fields_=[
            ("ob_base", type("PyObject", _bases, dict(_fields_=[
                ("ob_refcnt", ctypes.c_ssize_t),
                ("ob_type", ctypes.c_void_p),
            ]))),
            ("ob_size", ctypes.c_ssize_t),
        ]))),
        ("ob_digit", ctypes.c_uint32 * 1000),
    ])),
)


def inc(x: int) -> None:
    """Increment value of x by one.

    Note: if x is one less than 2 ^ (30 * n) (for n any positive
    integer), the integer may overflow to 0.

    Note: uses CPython (<= 3.10) long-integer internals. May not work
    in other implementations.
    """

    p = ctypes.cast(id(x), PyLongPointer)

    if p.contents.ob_base.ob_size > 0:
        amount = 1
        overflow = 2 ** 30
        reset = 0
    else:
        amount = -1
        overflow = 2 ** 32 - 1
        reset = 2 ** 30 - 1

    p.contents.ob_digit[0] += amount

    i = 0
    while p.contents.ob_digit[i] == overflow:
        p.contents.ob_digit[i] = reset

        i += 1
        if i < abs(p.contents.ob_base.ob_size):
            p.contents.ob_digit[i] += amount


a = 3
print(a)  # 3
inc(a)
print(a)  # 4

print(3)  # 4