does close() imply flush() in Python?
NB: close() and flush() won't ensure that the data is actually secure on the disk. It just ensures that the OS has the data == that it isn't buffered inside the process.
You can try sync or fsync to get the data written to the disk.
Yes, in Python 3 this is finally in the official documentation, but is was already the case in Python 2 (see Martin's answer).