Documentation

Doc/library/sys.rst says sys._clear_type_cache() clears the internal type cache, and that sys._clear_internal_caches() clears all internal performance-related caches. Neither does any more. Both reach it only through PyType_ClearCache(), which is now just return NEXT_VERSION_TAG(interp) - 1;.

import sys, _testinternalcapi

class C:
    x = 'v'

C.x                                        # populate the per-type lookup cache
print("cached:                          ", _testinternalcapi.type_cache_lookup(C, 'x'))
sys._clear_type_cache()
print("after sys._clear_type_cache:     ", _testinternalcapi.type_cache_lookup(C, 'x'))
sys._clear_internal_caches()
print("after sys._clear_internal_caches:", _testinternalcapi.type_cache_lookup(C, 'x'))

cached:                           (1, 'v', 131161)
after sys._clear_type_cache:      (1, 'v', 131161)
after sys._clear_internal_caches: (1, 'v', 131161)

The C API side is already documented. Doc/c-api/type.rst says the function is now a no-op, and GH-150160 added a matching porting note. The Python wrappers look like the spot that was missed.

Linked PRs

• gh-155354: Update sys._clear_type_cache() docs to reflect no-op #155378
• gh-155354: Document that sys no longer clears the type cache #155391