def _write(self, bytes):
        """
        Process the given application bytes and send any resulting TLS traffic
        which arrives in the send BIO.

        This may be called by C{dataReceived} with bytes that were buffered
        before C{loseConnection} was called, which is why this function
        doesn't check for disconnection but accepts the bytes regardless.
        """
        if self._lostTLSConnection:
            return

        # A TLS payload is 16kB max
        bufferSize = 2 ** 14

        # How far into the input we've gotten so far
        alreadySent = 0

        while alreadySent < len(bytes):
            toSend = bytes[alreadySent:alreadySent + bufferSize]
            try:
                sent = self._tlsConnection.send(toSend)
            except WantReadError:
                self._bufferedWrite(bytes[alreadySent:])
                break
            except Error:
                # Pretend TLS connection disconnected, which will trigger
                # disconnect of underlying transport. The error will be passed
                # to the application protocol's connectionLost method.  The
                # other SSL implementation doesn't, but losing helpful
                # debugging information is a bad idea.
                self._tlsShutdownFinished(Failure())
                break
            else:
                # We've successfully handed off the bytes to the OpenSSL
                # Connection object.
                alreadySent += sent
                # See if OpenSSL wants to hand any bytes off to the underlying
                # transport as a result.
                self._flushSendBIO()

        Process the given application bytes and send any resulting TLS traffic
        which arrives in the send BIO.

        This may be called by C{dataReceived} with bytes that were buffered
        before C{loseConnection} was called, which is why this function
        doesn't check for disconnection but accepts the bytes regardless.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/protocols/tls.py