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gh-87595: Fix size method on anonymous mmap object #138198

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gh-87595: Fix size method on anonymous mmap object #138198

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d82537c
Fix size method on anonymous mmap object
aisk Aug 27, 2025
4eb2eac
Add news entry
aisk Aug 27, 2025
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2 changes: 2 additions & 0 deletions Lib/test/test_mmap.py
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Expand Up @@ -506,6 +506,8 @@ def test_anonymous(self):
m[x] = b
self.assertEqual(m[x], b)

self.assertEqual(m.size(), PAGESIZE)

def test_read_all(self):
m = mmap.mmap(-1, 16)
self.addCleanup(m.close)
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2025-08-28-01-29-01.gh-issue-87595.Ncgrwo.rst
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@@ -0,0 +1 @@
Fix :meth:`mmap.mmap.size` method for anonymous mmap files on Unix.
3 changes: 3 additions & 0 deletions Modules/mmapmodule.c
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Expand Up @@ -747,6 +747,9 @@ mmap_size_method(PyObject *op, PyObject *Py_UNUSED(ignored))

#ifdef UNIX
{
if (self->trackfd && self->fd == -1) {
return PyLong_FromSsize_t(self->size);
}
struct _Py_stat_struct status;
if (_Py_fstat(self->fd, &status) == -1)
return NULL;
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