Class RawIOKeepsReference

Lib/test/test_io/test_general.py:615–625

        # gh-60107: Ensure a "Raw I/O" which keeps a reference to the
        # mutable memory doesn't allow making a mutable bytes.
        class RawIOKeepsReference(self.MockRawIOWithoutRead):
            def __init__(self, *args, **kwargs):
                self.buf = None
                super().__init__(*args, **kwargs)

            def readinto(self, buf):
                # buf is the bytearray so keeping a reference to it doesn't keep
                # the memory alive; a memoryview does.
                self.buf = memoryview(buf)
                buf[0:4] = self._read_stack.pop()
                return 3

        with self.assertRaises(BufferError):
            rawio = RawIOKeepsReference([b"1234"])