There are two uses for PyMem_SetAllocator():

1. set the allocator for the runtime to use
2. set an allocator hook that wraps the current allocator

The first must be done (only by embedders) "just after the pre-initialization, and before the Python initialization", while the second may be done at any point (e.g. by extension modules, like tracemalloc). See #96975 (comment).

The docs for PyMem_SetAllocator() should make the distinction more clear, as well as identifying the restriction on (1).

• PR: gh-96997: Clarify the contract of PyMem_SetAllocator() #98977

• PR: [3.11] gh-96997: Clarify the contract of PyMem_SetAllocator() (GH-98977) #99027

• PR: [3.10] gh-96997: Clarify the contract of PyMem_SetAllocator() (GH-98977) #99028