diff --git a/plugins/USBPrinting/USBPrinterOutputDevice.py b/plugins/USBPrinting/USBPrinterOutputDevice.py
index 421168b87f..af90961ff9 100644
--- a/plugins/USBPrinting/USBPrinterOutputDevice.py
+++ b/plugins/USBPrinting/USBPrinterOutputDevice.py
@@ -182,10 +182,10 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
 
         if len(hex_file) == 0:
             Logger.log("e", "Unable to read provided hex file. Could not update firmware")
-            return 
+            return
 
         programmer = stk500v2.Stk500v2()
-        programmer.progressCallback = self.setProgress
+        programmer.progress_callback = self.setProgress
 
         try:
             programmer.connect(self._serial_port)
@@ -197,7 +197,7 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
 
         if not programmer.isConnected():
             Logger.log("e", "Unable to connect with serial. Could not update firmware")
-            return 
+            return
 
         self._updating_firmware = True
 
@@ -299,7 +299,7 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
                         self.setConnectionState(ConnectionState.connected)
                         self._listen_thread.start()  # Start listening
                         Logger.log("i", "Established printer connection on port %s" % self._serial_port)
-                        return 
+                        return
 
                 self._sendCommand("M105")  # Send M105 as long as we are listening, otherwise we end up in an undefined state
 
@@ -327,7 +327,7 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
 
         self._connect_thread = threading.Thread(target = self._connect)
         self._connect_thread.daemon = True
-        
+
         self.setConnectionState(ConnectionState.closed)
         if self._serial is not None:
             try:
@@ -556,7 +556,7 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
             ret = self._serial.readline()
         except Exception as e:
             Logger.log("e", "Unexpected error while reading serial port. %s" % e)
-            self._setErrorState("Printer has been disconnected") 
+            self._setErrorState("Printer has been disconnected")
             self.close()
             return None
         return ret
diff --git a/plugins/USBPrinting/avr_isp/stk500v2.py b/plugins/USBPrinting/avr_isp/stk500v2.py
index 3960912e1d..afdb50553e 100644
--- a/plugins/USBPrinting/avr_isp/stk500v2.py
+++ b/plugins/USBPrinting/avr_isp/stk500v2.py
@@ -20,8 +20,8 @@ class Stk500v2(ispBase.IspBase):
         self.serial = None
         self.seq = 1
         self.last_addr = -1
-        self.progressCallback = None
-        
+        self.progress_callback = None
+
     def connect(self, port = "COM22", speed = 115200):
         if self.serial is not None:
             self.close()
@@ -69,7 +69,7 @@ class Stk500v2(ispBase.IspBase):
             self.serial = None
             return ret
         return None
-    
+
     def isConnected(self):
         return self.serial is not None
 
@@ -79,7 +79,7 @@ class Stk500v2(ispBase.IspBase):
     def sendISP(self, data):
         recv = self.sendMessage([0x1D, 4, 4, 0, data[0], data[1], data[2], data[3]])
         return recv[2:6]
-    
+
     def writeFlash(self, flash_data):
         #Set load addr to 0, in case we have more then 64k flash we need to enable the address extension
         page_size = self.chip["pageSize"] * 2
@@ -89,15 +89,15 @@ class Stk500v2(ispBase.IspBase):
             self.sendMessage([0x06, 0x80, 0x00, 0x00, 0x00])
         else:
             self.sendMessage([0x06, 0x00, 0x00, 0x00, 0x00])
-        load_count = (len(flash_data) + page_size - 1) / page_size   
+        load_count = (len(flash_data) + page_size - 1) / page_size
         for i in range(0, int(load_count)):
             recv = self.sendMessage([0x13, page_size >> 8, page_size & 0xFF, 0xc1, 0x0a, 0x40, 0x4c, 0x20, 0x00, 0x00] + flash_data[(i * page_size):(i * page_size + page_size)])
-            if self.progressCallback is not None:
+            if self.progress_callback is not None:
                 if self._has_checksum:
-                    self.progressCallback(i + 1, load_count)
+                    self.progress_callback(i + 1, load_count)
                 else:
-                    self.progressCallback(i + 1, load_count * 2)
-    
+                    self.progress_callback(i + 1, load_count * 2)
+
     def verifyFlash(self, flash_data):
         if self._has_checksum:
             self.sendMessage([0x06, 0x00, (len(flash_data) >> 17) & 0xFF, (len(flash_data) >> 9) & 0xFF, (len(flash_data) >> 1) & 0xFF])
@@ -120,8 +120,8 @@ class Stk500v2(ispBase.IspBase):
             load_count = (len(flash_data) + 0xFF) / 0x100
             for i in range(0, int(load_count)):
                 recv = self.sendMessage([0x14, 0x01, 0x00, 0x20])[2:0x102]
-                if self.progressCallback is not None:
-                    self.progressCallback(load_count + i + 1, load_count * 2)
+                if self.progress_callback is not None:
+                    self.progress_callback(load_count + i + 1, load_count * 2)
                 for j in range(0, 0x100):
                     if i * 0x100 + j < len(flash_data) and flash_data[i * 0x100 + j] != recv[j]:
                         raise ispBase.IspError("Verify error at: 0x%x" % (i * 0x100 + j))
@@ -141,7 +141,7 @@ class Stk500v2(ispBase.IspBase):
             raise ispBase.IspError("Serial send timeout")
         self.seq = (self.seq + 1) & 0xFF
         return self.recvMessage()
-    
+
     def recvMessage(self):
         state = "Start"
         checksum = 0