You're trying to create a tuple, but you're just parenthesizing a string :)
Add an extra ',':
dRecieved = connFile.readline()
processThread = threading.Thread(target=processLine, args=(dRecieved,)) # <- note extra ','
processThread.start()
Or use brackets to make a list:
dRecieved = connFile.readline()
processThread = threading.Thread(target=processLine, args=[dRecieved]) # <- 1 element list
processThread.start()
If you notice, from the stack trace: self.__target(*self.__args, **self.__kwargs)
The *self.__args turns your string into a list of characters, passing them to the processLine
function. If you pass it a one element list, it will pass that element as the first argument - in your case, the string.