mmap.flush returns the result of the call to FlushViewOfFile as an
integer, and does not check for errors. On unix it does check for
errors. The function should return None and raise an exception if an
error occurs...
This bug can lead to data loss...

Here's the current version of that function:

static PyObject *
mmap_flush_method(mmap_object *self, PyObject *args)
{
	Py_ssize_t offset = 0;
	Py_ssize_t size = self->size;
	CHECK_VALID(NULL);
	if (!PyArg_ParseTuple(args, "|nn:flush", &offset, &size))
		return NULL;
	if ((size_t)(offset + size) > self->size) {
		PyErr_SetString(PyExc_ValueError, "flush values out of range");
		return NULL;
	}
#ifdef MS_WINDOWS
	return PyInt_FromLong((long) FlushViewOfFile(self->data+offset, size));
#elif defined(UNIX)
	/* XXX semantics of return value? */
	/* XXX flags for msync? */
	if (-1 == msync(self->data + offset, size, MS_SYNC)) {
		PyErr_SetFromErrno(mmap_module_error);
		return NULL;
	}
	return PyInt_FromLong(0);
#else
	PyErr_SetString(PyExc_ValueError, "flush not supported on this system");
	return NULL;
#endif
}