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Hi.
the file and line arguments are for expanding from macros such as PyMem_MALLOC. I had them added because they provide the features of a comprehensive debugging API.
Of course, I'm not showing you the entire set of modifications that we have made to the memory allocation scheme. They including more extensive versions of the memory allocation tools, in order to more easily monitor memory allocations from within C.
For your information, I'm uploading pymemory.h from our 2.7 patch. The extent of our modifications can be gleaned from there.
Basically, we have layered the macros into outer and inner versions, in order to better support internal diagnostics.
I'm happy with the api you provide, with a small addition:
PyAPI_FUNC(int) Py_SetAllocators(
 char api,
 void* (*malloc) (size_t size, void *data),
 void* (*realloc) (void* ptr, size_t size, void *data),
 void (*free) (void* ptr, void *data),
 void *data
 );
The 'data' pointer is pointless unless you can provide it as part of the api. This sort of extra indirection is necessary for C callbacks to provide instance specific context to statically compiled and linked callback functions.