def open(self):
        if self._port is None:
            raise SerialException("Port must be configured before it can be used.")
        if self.is_open:
            raise SerialException("Port is already open.")
        # if RTS and/or DTR are not set before open, they default to True
        if self._rts_state is None:
            self._rts_state = True
        if self._dtr_state is None:
            self._dtr_state = True
        # the "\\.\COMx" format is required for devices other than COM1-COM8
        # not all versions of windows seem to support this properly
        # so that the first few ports are used with the DOS device name
        port = self.name
        try:
            if port.upper().startswith('COM') and int(port[3:]) > 8:
                port = '\\\\.\\' + port
        except ValueError:
            # for like COMnotanumber
            pass
        self._port_handle = win32.CreateFile(
            port,
            win32.GENERIC_READ | win32.GENERIC_WRITE,
            0,  # exclusive access
            None,  # no security
            win32.OPEN_EXISTING,
            win32.FILE_ATTRIBUTE_NORMAL | win32.FILE_FLAG_OVERLAPPED,
            0)
        if self._port_handle == win32.INVALID_HANDLE_VALUE:
            self._port_handle = None    # 'cause __del__ is called anyway
            raise SerialException("could not open port {!r}: {!r}".format(self.portstr, ctypes.WinError()))

        try:
            self._overlapped_read = win32.OVERLAPPED()
            self._overlapped_read.hEvent = win32.CreateEvent(None, 1, 0, None)
            self._overlapped_write = win32.OVERLAPPED()
            #~ self._overlapped_write.hEvent = win32.CreateEvent(None, 1, 0, None)
            self._overlapped_write.hEvent = win32.CreateEvent(None, 0, 0, None)

            # Setup a 4k buffer
            win32.SetupComm(self._port_handle, 4096, 4096)

            # Save original timeout values:
            self._orgTimeouts = win32.COMMTIMEOUTS()
            win32.GetCommTimeouts(self._port_handle, ctypes.byref(self._orgTimeouts))

            self._reconfigure_port()

            # Clear buffers:
            # Remove anything that was there
            win32.PurgeComm(
                self._port_handle,
                win32.PURGE_TXCLEAR | win32.PURGE_TXABORT |
                win32.PURGE_RXCLEAR | win32.PURGE_RXABORT)
        except:
            try:
                self._close()
            except:
                # ignore any exception when closing the port
                # also to keep original exception that happened when setting up
                pass
            self._port_handle = None
            raise
        else:
            self.is_open = True
Open port with current settings. This may throw a SerialException
dataset/ETHPy150Open pyserial/pyserial/serial/serialwin32.py/Serial.open