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[C API] Change PyTypeObject.tp_flags type to uint64_t #161562
Description
Feature or enhancement
Currently, PyTypeObject.tp_flags type is unsigned long which is 32-bit on Windows and 32-bit platforms. There are less and less available type flags: https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_flags.
I propose extending PyTypeObject.tp_flags to uint64_t to get 32 additional flags.
Has this already been discussed elsewhere?
I have already discussed this feature proposal on Discourse
Links to previous discussion of this feature:
The issue was discussed at We’re out of type flags, let’s add new API for new ones.
Activity
pythongh-161562: Change PyTypeObject.tp_flags type to uint64_t
pythongh-161562: Change PyTypeObject.tp_flags type to uint64_t
ronaldoussoren commentedon Nov 8, 2026
Isn't this a duplicate for #134860?
As mentioned in that issue: Flags are also an unsigned int in PyType_Spec, which is part of the stable ABI. See https://docs.python.org/3/c-api/type.html#c.PyType_Spec.flags
Likewise for PyType_GetFlags where the return value is an unsigned long (32-bit on 32-bit platforms, and on 64-bit windows)
vstinner commentedon Nov 8, 2026
Oh, I wasn't aware of this issue. Well, this issue is a concrete change to implement the "Change PyTypeObject.tp_flags type to uint64_t" option.
The updated PyType_Spec documentation in the PR suggest using
PyType_FromSlots()if you need 64-bit flags. If you don't need new 64-bit flags, it's fine to still use PyType_Spec().With my change, PyType_GetFlags() return type changes to uint64_t when using non-limited C API or when using the limited C API version 3.16 or newer. It stays as
unsigned longwhen using the limited C API version 3.15 or newer (stable ABI!). See the PR for details.