Closes #15488: Closed files keep their buffer alive

Lib/test/test_io.py

@@ -815,6 +815,14 @@ class SizeofTest:
         bufio = self.tp(rawio, buffer_size=bufsize2)
         self.assertEqual(sys.getsizeof(bufio), size + bufsize2)
 
+    @support.cpython_only
+    def test_buffer_freeing(self) :
+        bufsize = 4096
+        rawio = self.MockRawIO()
+        bufio = self.tp(rawio, buffer_size=bufsize)
+        size = sys.getsizeof(bufio) - bufsize
+        bufio.close()
+        self.assertEqual(sys.getsizeof(bufio), size)
 
 class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
     read_mode = "rb"

Misc/NEWS

@@ -24,6 +24,9 @@ Core and Builtins
 
 - Issue #15839: Convert SystemErrors in `super()` to RuntimeErrors.
 
+- Issue #15448: Buffered IO now frees the buffer when closed, instead
+  of when deallocating.
+
 - Issue #15846: Fix SystemError which happened when using `ast.parse()` in an
   exception handler on code with syntax errors.
 

Modules/_io/bufferedio.c

@@ -519,6 +519,11 @@ buffered_close(buffered *self, PyObject *args)
 
     res = PyObject_CallMethodObjArgs(self->raw, _PyIO_str_close, NULL);
 
+    if (self->buffer) {
+        PyMem_Free(self->buffer);
+        self->buffer = NULL;
+    }
+
 end:
     LEAVE_BUFFERED(self)
     return res;