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gh-107940: Only reuse the pointer object when it matches the _type_ of the container #108222

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gh-107940: Only reuse the pointer object when it matches the _type_ of the container #108222

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Only reuse the pointer object when it matches the `_type_` of the con…
ambv Aug 15, 2023
d2ff7a4
WIP
ambv Aug 23, 2023
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@ambv
ambv committed Aug 24, 2023
commit d2ff7a4cc9a85cedb3db4a8c405fac157936c720
29 changes: 29 additions & 0 deletions Lib/test/test_ctypes/test_cast.py
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Original file line number Diff line number Diff line change
Expand Up @@ -160,6 +160,35 @@ class StructWithPointers(Structure):
self.assertEqual(obj[0].contents.a, 10)
self.assertEqual(obj[1].contents.a, 20)

def test_pointer_set_contents(self):
class Struct(Structure):
_fields_ = [('a', c_int16)]
p = pointer(Struct(a=23))
self.assertEqual(p.contents.a, 23)
self.assertIs(p._type_, Struct)
cp = cast(p, POINTER(c_int16))
self.assertEqual(cp.contents._type_, 'h')
cp.contents = c_int16(24)
self.assertEqual(cp.contents.value, 24)
self.assertEqual(p.contents.a, 24)

pp = pointer(p)
self.assertIs(pp._type_, POINTER(Struct))

from code import interact; interact(local=locals())

cast(pp, POINTER(POINTER(c_int16))).contents.contents = c_int16(32)

# self.assertIs(p.contents, pp.contents.contents)

self.assertEqual(cast(p, POINTER(c_int16)).contents.value, 32)
self.assertEqual(p[0].a, 32) # works
self.assertEqual(pp[0].contents.a, 32) # works
self.assertEqual(pp.contents[0].a, 32) # works

self.assertEqual(p.contents.a, 32) # fails, wat, holds 23
self.assertEqual(pp.contents.contents.a, 32) # fails, wat, holds 23


if __name__ == "__main__":
unittest.main()
12 changes: 8 additions & 4 deletions Modules/_ctypes/_ctypes.c
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Expand Up @@ -5172,11 +5172,15 @@ Pointer_get_contents(CDataObject *self, void *closure)
// It's not a cast: don't construct a new object,
// return existing one instead to preserve refcount
p2p = (CDataObject*) ptr2ptr;
printf("self->b_ptr=%lu\n", *(void**) self->b_ptr);
printf("p2p->b_ptr=%lu\n", *(void**) p2p->b_ptr);
printf("self->b_value.c=%lu\n", *(void**) self->b_value.c);
printf("p2p->b_value.c=%lu\n", *(void**) p2p->b_value.c);
assert(
*(void**) self->b_ptr == p2p->b_ptr ||
*(void**) self->b_value.c == p2p->b_ptr ||
*(void**) self->b_ptr == p2p->b_value.c ||
*(void**) self->b_value.c == p2p->b_value.c
*(void**) self->b_ptr == *(void**) p2p->b_ptr ||
*(void**) self->b_value.c == *(void**) p2p->b_ptr ||
*(void**) self->b_ptr == *(void**) p2p->b_value.c ||
*(void**) self->b_value.c == *(void**) p2p->b_value.c
); // double-check that we are returning the same thing
Py_INCREF(ptr2ptr);
return ptr2ptr;
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