minor changes

examples/read_card.py

@@ -160,7 +160,7 @@ class CardReader:
             else:
                 return(ERROR_READER_READ)
 
-    def doOp(self,  opCode, opParmStr, opParmLen, timeout=None):
+    def doOp(self,  opCode, opParmStr=None, opParmLen=0, timeout=None):
         self.serCon.ser.timeout = timeout
         self.write(opCode, opParmStr, opParmLen)
         self.returnMsg = ''
@@ -196,6 +196,6 @@ if __name__ == "__main__":
         print(cardReader.getReturnMsg())
         sys.exit()
     # actSeconds = str(int(time.time()))
-    cardReader.doOp(f'01',None,0)
+    cardReader.doOp(f'01')
     print(cardReader.getReturnCode(),cardReader.getReturnMsg())
     cardReader.clear()
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