See discussion on https://github.com/LonamiWebs/Telethon/commit/49713b2.
The problem with the automatic approach is that some scripts may do
some "fancier" things with the way they register updates, so it was
prone to failure (a handler could be added but since the last request
was without updates, nothing would be received).
This new approach is a bit more annoying to opt-into but also more
explicit.
It was added back in bfc408b probably due to a misunderstanding of
https://docs.python.org/3/howto/logging.html#configuring-logging-for-a-library.
The default behaviour of logging WARNING and above is good and
desirable (hiding unhandled exceptions in update handlers by default
was a big, accidental mistake). NullHandler is used to *prevent*
this good default, so it shouldn't be used in the first place.
Borrowed senders are not disconnected immediately, but after a while.
If a borrow was used recently but the user requested the main client
to disconnect, those borrows "shouldn't" disconnect because they were
used recently. However, if the user requests a disconnect, they mean
that EVERYTHING should be disconnected, even if the borrows are recent.
This actually gets rid of warnings about send/recv tasks being destroyed,
which partially addresses #1634. That issue may still have more causes
though.
This behaviour is deprecated and will be removed in future versions
of Python. Technically, it could be considered a bug (invalid usage
causing different behaviour from the expected one), and in practice
it should not break much code (because .get_event_loop() would likely
be the same event loop anyway).
Which leads to "RuntimeError: readexactly() called while another
coroutine is already waiting for incoming data" being raised,
and causing everything to break or halt.
This way it is easy and cheap to copy the two required values
to all incoming updates in case we need to getDifference since
the previous pts/date to fetch entities.
This is still a work in progress.
