diff --git a/serial/rfc2217.py b/serial/rfc2217.py
index 119f039..a9b285a 100644
--- a/serial/rfc2217.py
+++ b/serial/rfc2217.py
@@ -260,7 +260,7 @@
 
     def __repr__(self):
         """String for debug outputs"""
-        return "%s:%s(%s)" % (self.name, self.active, self.state)
+        return "{o.name}:{o.active}({o.state})".format(o=self)
 
     def process_incoming(self, command):
         """\
@@ -284,7 +284,7 @@
             elif self.state is REALLY_INACTIVE:
                 self.connection.telnetSendOption(self.send_no, self.option)
             else:
-                raise ValueError('option in illegal state %r' % self)
+                raise ValueError('option in illegal state {!r}'.format(self))
         elif command == self.ack_no:
             if self.state is REQUESTED:
                 self.state = INACTIVE
@@ -298,7 +298,7 @@
             elif self.state is REALLY_INACTIVE:
                 pass
             else:
-                raise ValueError('option in illegal state %r' % self)
+                raise ValueError('option in illegal state {!r}'.format(self))
 
 
 class TelnetSubnegotiation(object):
@@ -319,7 +319,7 @@
 
     def __repr__(self):
         """String for debug outputs."""
-        return "%s:%s" % (self.name, self.state)
+        return "{sn.name}:{sn.state}".format(sn=self)
 
     def set(self, value):
         """\
@@ -331,7 +331,7 @@
         self.state = REQUESTED
         self.connection.rfc2217SendSubnegotiation(self.option, self.value)
         if self.connection.logger:
-            self.connection.logger.debug("SB Requesting %s -> %r" % (self.name, self.value))
+            self.connection.logger.debug("SB Requesting {} -> {!r}".format(self.name, self.value))
 
     def isReady(self):
         """\
@@ -339,7 +339,7 @@
         the change, raise a ValueError.
         """
         if self.state == REALLY_INACTIVE:
-            raise ValueError("remote rejected value for option %r" % (self.name))
+            raise ValueError("remote rejected value for option {!r}".format(self.name))
         return self.state == ACTIVE
     # add property to have a similar interface as TelnetOption
     active = property(isReady)
@@ -356,7 +356,7 @@
             if self.isReady():
                 break
         else:
-            raise SerialException("timeout while waiting for option %r" % (self.name))
+            raise SerialException("timeout while waiting for option {!r}".format(self.name))
 
     def checkAnswer(self, suboption):
         """\
@@ -369,7 +369,7 @@
             # error propagation done in isReady
             self.state = REALLY_INACTIVE
         if self.connection.logger:
-            self.connection.logger.debug("SB Answer %s -> %r -> %s" % (self.name, suboption, self.state))
+            self.connection.logger.debug("SB Answer {} -> {!r} -> {}".format(self.name, suboption, self.state))
 
 
 class Serial(SerialBase):
@@ -401,7 +401,7 @@
             self._socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
         except Exception as msg:
             self._socket = None
-            raise SerialException("Could not open port %s: %s" % (self.portstr, msg))
+            raise SerialException("Could not open port {}: {}".format(self.portstr, msg))
 
         self._socket.settimeout(5)  # XXX good value?
 
@@ -449,7 +449,7 @@
         self.is_open = True
         self._thread = threading.Thread(target=self._telnetReadLoop)
         self._thread.setDaemon(True)
-        self._thread.setName('pySerial RFC 2217 reader thread for %s' % (self._port,))
+        self._thread.setName('pySerial RFC 2217 reader thread for {}'.format(self._port))
         self._thread.start()
 
         try:    # must clean-up if open fails
@@ -464,9 +464,9 @@
                 if sum(o.active for o in mandadory_options) == sum(o.state != INACTIVE for o in mandadory_options):
                     break
             else:
-                raise SerialException("Remote does not seem to support RFC2217 or BINARY mode %r" % mandadory_options)
+                raise SerialException("Remote does not seem to support RFC2217 or BINARY mode {!r}".format(mandadory_options))
             if self.logger:
-                self.logger.info("Negotiated options: %s" % self._telnet_options)
+                self.logger.info("Negotiated options: {}".format(self._telnet_options))
 
             # fine, go on, set RFC 2271 specific things
             self._reconfigure_port()
@@ -496,7 +496,7 @@
         # Setup the connection
         # to get good performance, all parameter changes are sent first...
         if not 0 < self._baudrate < 2 ** 32:
-            raise ValueError("invalid baudrate: %r" % (self._baudrate))
+            raise ValueError("invalid baudrate: {!r}".format(self._baudrate))
         self._rfc2217_port_settings['baudrate'].set(struct.pack(b'!I', self._baudrate))
         self._rfc2217_port_settings['datasize'].set(struct.pack(b'!B', self._bytesize))
         self._rfc2217_port_settings['parity'].set(struct.pack(b'!B', RFC2217_PARITY_MAP[self._parity]))
@@ -505,16 +505,16 @@
         # and now wait until parameters are active
         items = self._rfc2217_port_settings.values()
         if self.logger:
-            self.logger.debug("Negotiating settings: %s" % (items,))
+            self.logger.debug("Negotiating settings: {}".format(items))
         timeout_time = time.time() + self._network_timeout
         while time.time() < timeout_time:
             time.sleep(0.05)    # prevent 100% CPU load
             if sum(o.active for o in items) == len(items):
                 break
         else:
-            raise SerialException("Remote does not accept parameter change (RFC2217): %r" % items)
+            raise SerialException("Remote does not accept parameter change (RFC2217): {!r}".format(items))
         if self.logger:
-            self.logger.info("Negotiated settings: %s" % (items,))
+            self.logger.info("Negotiated settings: {}".format(items))
 
         if self._rtscts and self._xonxoff:
             raise ValueError('xonxoff and rtscts together are not supported')
@@ -546,7 +546,10 @@
         """extract host and port from an URL string"""
         parts = urlparse.urlsplit(url)
         if parts.scheme != "rfc2217":
-            raise SerialException('expected a string in the form "rfc2217://<host>:<port>[?option[&option...]]": not starting with rfc2217:// (%r)' % (parts.scheme,))
+            raise SerialException(
+                'expected a string in the form '
+                '"rfc2217://<host>:<port>[?option[&option...]]": '
+                'not starting with rfc2217:// ({!r})'.format(parts.scheme))
         try:
             # process options now, directly altering self
             for option, values in urlparse.parse_qs(parts.query, True).items():
@@ -562,13 +565,15 @@
                 elif option == 'timeout':
                     self._network_timeout = float(values[0])
                 else:
-                    raise ValueError('unknown option: %r' % (option,))
+                    raise ValueError('unknown option: {!r}'.format(option))
             # get host and port
             host, port = parts.hostname, parts.port
             if not 0 <= port < 65536:
                 raise ValueError("port not in range 0...65535")
         except ValueError as e:
-            raise SerialException('expected a string in the form "rfc2217://<host>:<port>[?option[&option...]]": %s' % e)
+            raise SerialException(
+                'expected a string in the form '
+                '"rfc2217://<host>:<port>[?option[&option...]]": {}'.format(e))
         return (host, port)
 
     #  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -
@@ -610,7 +615,7 @@
             try:
                 self._socket.sendall(to_bytes(data).replace(IAC, IAC_DOUBLED))
             except socket.error as e:
-                raise SerialException("connection failed (socket error): %s" % (e,))
+                raise SerialException("connection failed (socket error): {}".format(e))
         return len(data)
 
     def reset_input_buffer(self):
@@ -639,7 +644,7 @@
         if not self.is_open:
             raise portNotOpenError
         if self.logger:
-            self.logger.info('set BREAK to %s' % ('active' if self._break_state else 'inactive'))
+            self.logger.info('set BREAK to {}'.format('active' if self._break_state else 'inactive'))
         if self._break_state:
             self.rfc2217SetControl(SET_CONTROL_BREAK_ON)
         else:
@@ -650,7 +655,7 @@
         if not self.is_open:
             raise portNotOpenError
         if self.logger:
-            self.logger.info('set RTS to %s' % ('active' if self._rts_state else 'inactive'))
+            self.logger.info('set RTS to {}'.format('active' if self._rts_state else 'inactive'))
         if self._rts_state:
             self.rfc2217SetControl(SET_CONTROL_RTS_ON)
         else:
@@ -661,7 +666,7 @@
         if not self.is_open:
             raise portNotOpenError
         if self.logger:
-            self.logger.info('set DTR to %s' % ('active' if self._dtr_state else 'inactive'))
+            self.logger.info('set DTR to {}'.format('active' if self._dtr_state else 'inactive'))
         if self._dtr_state:
             self.rfc2217SetControl(SET_CONTROL_DTR_ON)
         else:
@@ -715,7 +720,7 @@
                 except socket.error as e:
                     # connection fails -> terminate loop
                     if self.logger:
-                        self.logger.debug("socket error in reader thread: %s" % (e,))
+                        self.logger.debug("socket error in reader thread: {}".format(e))
                     break
                 if not data:
                     break  # lost connection
@@ -771,7 +776,7 @@
         """Process commands other than DO, DONT, WILL, WONT."""
         # Currently none. RFC2217 only uses negotiation and subnegotiation.
         if self.logger:
-            self.logger.warning("ignoring Telnet command: %r" % (command,))
+            self.logger.warning("ignoring Telnet command: {!r}".format(command))
 
     def _telnetNegotiateOption(self, command, option):
         """Process incoming DO, DONT, WILL, WONT."""
@@ -790,7 +795,7 @@
             if command == WILL or command == DO:
                 self.telnetSendOption((DONT if command == WILL else WONT), option)
                 if self.logger:
-                    self.logger.warning("rejected Telnet option: %r" % (option,))
+                    self.logger.warning("rejected Telnet option: {!r}".format(option))
 
     def _telnetProcessSubnegotiation(self, suboption):
         """Process subnegotiation, the data between IAC SB and IAC SE."""
@@ -798,11 +803,11 @@
             if suboption[1:2] == SERVER_NOTIFY_LINESTATE and len(suboption) >= 3:
                 self._linestate = ord(suboption[2:3])  # ensure it is a number
                 if self.logger:
-                    self.logger.info("NOTIFY_LINESTATE: %s" % self._linestate)
+                    self.logger.info("NOTIFY_LINESTATE: {}".format(self._linestate))
             elif suboption[1:2] == SERVER_NOTIFY_MODEMSTATE and len(suboption) >= 3:
                 self._modemstate = ord(suboption[2:3])  # ensure it is a number
                 if self.logger:
-                    self.logger.info("NOTIFY_MODEMSTATE: %s" % self._modemstate)
+                    self.logger.info("NOTIFY_MODEMSTATE: {}".format(self._modemstate))
                 # update time when we think that a poll would make sense
                 self._modemstate_expires = time.time() + 0.3
             elif suboption[1:2] == FLOWCONTROL_SUSPEND:
@@ -817,10 +822,10 @@
                         break
                 else:
                     if self.logger:
-                        self.logger.warning("ignoring COM_PORT_OPTION: %r" % (suboption,))
+                        self.logger.warning("ignoring COM_PORT_OPTION: {!r}".format(suboption))
         else:
             if self.logger:
-                self.logger.warning("ignoring subnegotiation: %r" % (suboption,))
+                self.logger.warning("ignoring subnegotiation: {!r}".format(suboption))
 
     # - outgoing telnet commands and options
 
@@ -999,7 +1004,7 @@
                         SERVER_NOTIFY_MODEMSTATE,
                         to_bytes([modemstate & self.modemstate_mask]))
                 if self.logger:
-                    self.logger.info("NOTIFY_MODEMSTATE: %s" % (modemstate,))
+                    self.logger.info("NOTIFY_MODEMSTATE: {}".format(modemstate))
             # save last state, but forget about deltas.
             # otherwise it would also notify about changing deltas which is
             # probably not very useful
@@ -1087,7 +1092,7 @@
         """Process commands other than DO, DONT, WILL, WONT."""
         # Currently none. RFC2217 only uses negotiation and subnegotiation.
         if self.logger:
-            self.logger.warning("ignoring Telnet command: %r" % (command,))
+            self.logger.warning("ignoring Telnet command: {!r}".format(command))
 
     def _telnetNegotiateOption(self, command, option):
         """Process incoming DO, DONT, WILL, WONT."""
@@ -1106,13 +1111,13 @@
             if command == WILL or command == DO:
                 self.telnetSendOption((DONT if command == WILL else WONT), option)
                 if self.logger:
-                    self.logger.warning("rejected Telnet option: %r" % (option,))
+                    self.logger.warning("rejected Telnet option: {!r}".format(option))
 
     def _telnetProcessSubnegotiation(self, suboption):
         """Process subnegotiation, the data between IAC SB and IAC SE."""
         if suboption[0:1] == COM_PORT_OPTION:
             if self.logger:
-                self.logger.debug('received COM_PORT_OPTION: %r' % (suboption,))
+                self.logger.debug('received COM_PORT_OPTION: {!r}'.format(suboption))
             if suboption[1:2] == SET_BAUDRATE:
                 backup = self.serial.baudrate
                 try:
@@ -1121,11 +1126,11 @@
                         self.serial.baudrate = baudrate
                 except ValueError as e:
                     if self.logger:
-                        self.logger.error("failed to set baud rate: %s" % (e,))
+                        self.logger.error("failed to set baud rate: {}".format(e))
                     self.serial.baudrate = backup
                 else:
                     if self.logger:
-                        self.logger.info("%s baud rate: %s" % ('set' if baudrate else 'get', self.serial.baudrate))
+                        self.logger.info("{} baud rate: {}".format('set' if baudrate else 'get', self.serial.baudrate))
                 self.rfc2217SendSubnegotiation(SERVER_SET_BAUDRATE, struct.pack(b"!I", self.serial.baudrate))
             elif suboption[1:2] == SET_DATASIZE:
                 backup = self.serial.bytesize
@@ -1135,11 +1140,11 @@
                         self.serial.bytesize = datasize
                 except ValueError as e:
                     if self.logger:
-                        self.logger.error("failed to set data size: %s" % (e,))
+                        self.logger.error("failed to set data size: {}".format(e))
                     self.serial.bytesize = backup
                 else:
                     if self.logger:
-                        self.logger.info("%s data size: %s" % ('set' if datasize else 'get', self.serial.bytesize))
+                        self.logger.info("{} data size: {}".format('set' if datasize else 'get', self.serial.bytesize))
                 self.rfc2217SendSubnegotiation(SERVER_SET_DATASIZE, struct.pack(b"!B", self.serial.bytesize))
             elif suboption[1:2] == SET_PARITY:
                 backup = self.serial.parity
@@ -1149,11 +1154,11 @@
                             self.serial.parity = RFC2217_REVERSE_PARITY_MAP[parity]
                 except ValueError as e:
                     if self.logger:
-                        self.logger.error("failed to set parity: %s" % (e,))
+                        self.logger.error("failed to set parity: {}".format(e))
                     self.serial.parity = backup
                 else:
                     if self.logger:
-                        self.logger.info("%s parity: %s" % ('set' if parity else 'get', self.serial.parity))
+                        self.logger.info("{} parity: {}".format('set' if parity else 'get', self.serial.parity))
                 self.rfc2217SendSubnegotiation(
                         SERVER_SET_PARITY,
                         struct.pack(b"!B", RFC2217_PARITY_MAP[self.serial.parity]))
@@ -1165,11 +1170,11 @@
                         self.serial.stopbits = RFC2217_REVERSE_STOPBIT_MAP[stopbits]
                 except ValueError as e:
                     if self.logger:
-                        self.logger.error("failed to set stop bits: %s" % (e,))
+                        self.logger.error("failed to set stop bits: {}".format(e))
                     self.serial.stopbits = backup
                 else:
                     if self.logger:
-                        self.logger.info("%s stop bits: %s" % ('set' if stopbits else 'get', self.serial.stopbits))
+                        self.logger.info("{} stop bits: {}".format('set' if stopbits else 'get', self.serial.stopbits))
                 self.rfc2217SendSubnegotiation(
                         SERVER_SET_STOPSIZE,
                         struct.pack(b"!B", RFC2217_STOPBIT_MAP[self.serial.stopbits]))
@@ -1268,11 +1273,11 @@
             elif suboption[1:2] == SET_LINESTATE_MASK:
                 self.linstate_mask = ord(suboption[2:3])  # ensure it is a number
                 if self.logger:
-                    self.logger.info("line state mask: 0x%02x" % (self.linstate_mask,))
+                    self.logger.info("line state mask: 0x{:02x}".format(self.linstate_mask))
             elif suboption[1:2] == SET_MODEMSTATE_MASK:
                 self.modemstate_mask = ord(suboption[2:3])  # ensure it is a number
                 if self.logger:
-                    self.logger.info("modem state mask: 0x%02x" % (self.modemstate_mask,))
+                    self.logger.info("modem state mask: 0x{:02x}".format(self.modemstate_mask))
             elif suboption[1:2] == PURGE_DATA:
                 if suboption[2:3] == PURGE_RECEIVE_BUFFER:
                     self.serial.reset_input_buffer()
@@ -1292,23 +1297,23 @@
                     self.rfc2217SendSubnegotiation(SERVER_PURGE_DATA, PURGE_BOTH_BUFFERS)
                 else:
                     if self.logger:
-                        self.logger.error("undefined PURGE_DATA: %r" % list(suboption[2:]))
+                        self.logger.error("undefined PURGE_DATA: {!r}".format(list(suboption[2:])))
             else:
                 if self.logger:
-                    self.logger.error("undefined COM_PORT_OPTION: %r" % list(suboption[1:]))
+                    self.logger.error("undefined COM_PORT_OPTION: {!r}".format(list(suboption[1:])))
         else:
             if self.logger:
-                self.logger.warning("unknown subnegotiation: %r" % (suboption,))
+                self.logger.warning("unknown subnegotiation: {!r}".format(suboption))
 
 
 # simple client test
 if __name__ == '__main__':
     import sys
     s = Serial('rfc2217://localhost:7000', 115200)
-    sys.stdout.write('%s\n' % s)
+    sys.stdout.write('{}\n'.format(s))
 
     sys.stdout.write("write...\n")
     s.write(b"hello\n")
     s.flush()
-    sys.stdout.write("read: %s\n" % s.read(5))
+    sys.stdout.write("read: {}\n".format(s.read(5)))
     s.close()
diff --git a/serial/serialwin32.py b/serial/serialwin32.py
index e2fe7f3..f33bee5 100644
--- a/serial/serialwin32.py
+++ b/serial/serialwin32.py
@@ -64,7 +64,7 @@
             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" % (self.portstr, ctypes.WinError()))
+            raise SerialException("could not open port {!r}: {!r}".format(self.portstr, ctypes.WinError()))
 
         try:
             self._overlapped_read = win32.OVERLAPPED()
@@ -145,7 +145,7 @@
         elif self._bytesize == serial.EIGHTBITS:
             comDCB.ByteSize = 8
         else:
-            raise ValueError("Unsupported number of data bits: %r" % self._bytesize)
+            raise ValueError("Unsupported number of data bits: {!r}".format(self._bytesize))
 
         if self._parity == serial.PARITY_NONE:
             comDCB.Parity = win32.NOPARITY
@@ -163,7 +163,7 @@
             comDCB.Parity = win32.SPACEPARITY
             comDCB.fParity = 1  # Enable Parity Check
         else:
-            raise ValueError("Unsupported parity mode: %r" % self._parity)
+            raise ValueError("Unsupported parity mode: {!r}".format(self._parity))
 
         if self._stopbits == serial.STOPBITS_ONE:
             comDCB.StopBits = win32.ONESTOPBIT
@@ -172,7 +172,7 @@
         elif self._stopbits == serial.STOPBITS_TWO:
             comDCB.StopBits = win32.TWOSTOPBITS
         else:
-            raise ValueError("Unsupported number of stop bits: %r" % self._stopbits)
+            raise ValueError("Unsupported number of stop bits: {!r}".format(self._stopbits))
 
         comDCB.fBinary = 1  # Enable Binary Transmission
         # Char. w/ Parity-Err are replaced with 0xff (if fErrorChar is set to TRUE)
@@ -187,24 +187,24 @@
             # XXX verify if platform really does not have a setting for those
             if not self._rs485_mode.rts_level_for_tx:
                 raise ValueError(
-                        'Unsupported value for RS485Settings.rts_level_for_tx: %r' % (
-                            self._rs485_mode.rts_level_for_tx,))
+                    'Unsupported value for RS485Settings.rts_level_for_tx: {!r}'.format(
+                        self._rs485_mode.rts_level_for_tx,))
             if self._rs485_mode.rts_level_for_rx:
                 raise ValueError(
-                        'Unsupported value for RS485Settings.rts_level_for_rx: %r' % (
-                            self._rs485_mode.rts_level_for_rx,))
+                    'Unsupported value for RS485Settings.rts_level_for_rx: {!r}'.format(
+                        self._rs485_mode.rts_level_for_rx,))
             if self._rs485_mode.delay_before_tx is not None:
                 raise ValueError(
-                        'Unsupported value for RS485Settings.delay_before_tx: %r' % (
-                            self._rs485_mode.delay_before_tx,))
+                    'Unsupported value for RS485Settings.delay_before_tx: {!r}'.format(
+                        self._rs485_mode.delay_before_tx,))
             if self._rs485_mode.delay_before_rx is not None:
                 raise ValueError(
-                        'Unsupported value for RS485Settings.delay_before_rx: %r' % (
-                            self._rs485_mode.delay_before_rx,))
+                    'Unsupported value for RS485Settings.delay_before_rx: {!r}'.format(
+                        self._rs485_mode.delay_before_rx,))
             if self._rs485_mode.loopback:
                 raise ValueError(
-                        'Unsupported value for RS485Settings.loopback: %r' % (
-                            self._rs485_mode.loopback,))
+                    'Unsupported value for RS485Settings.loopback: {!r}'.format(
+                        self._rs485_mode.loopback,))
             comDCB.fRtsControl = win32.RTS_CONTROL_TOGGLE
             comDCB.fOutxCtsFlow = 0
 
@@ -222,7 +222,9 @@
         comDCB.XoffChar = serial.XOFF
 
         if not win32.SetCommState(self._port_handle, ctypes.byref(comDCB)):
-            raise SerialException("Cannot configure port, something went wrong. Original message: %r" % ctypes.WinError())
+            raise SerialException(
+                'Cannot configure port, something went wrong. '
+                'Original message: {!r}'.format(ctypes.WinError()))
 
     #~ def __del__(self):
         #~ self.close()
@@ -283,7 +285,7 @@
                     ctypes.byref(rc),
                     ctypes.byref(self._overlapped_read))
                 if not read_ok and win32.GetLastError() not in (win32.ERROR_SUCCESS, win32.ERROR_IO_PENDING):
-                    raise SerialException("ReadFile failed (%r)" % ctypes.WinError())
+                    raise SerialException("ReadFile failed ({!r})".format(ctypes.WinError()))
                 win32.GetOverlappedResult(
                     self._port_handle,
                     ctypes.byref(self._overlapped_read),
@@ -309,7 +311,7 @@
             n = win32.DWORD()
             err = win32.WriteFile(self._port_handle, data, len(data), ctypes.byref(n), self._overlapped_write)
             if not err and win32.GetLastError() != win32.ERROR_IO_PENDING:
-                raise SerialException("WriteFile failed (%r)" % ctypes.WinError())
+                raise SerialException("WriteFile failed ({!r})".format(ctypes.WinError()))
             if self._write_timeout != 0:  # if blocking (None) or w/ write timeout (>0)
                 # Wait for the write to complete.
                 #~ win32.WaitForSingleObject(self._overlapped_write.hEvent, win32.INFINITE)