I have a pretty basic point of confusion that I'm hoping I can have explained to me. I have a class in which I want to override a method, and have my method defined externally to the class definition invoked instead. But when I do so, my external method is invoked with a different argument signature than the method it overrides.

(I'll illustrate with a toy example named toy.py that maintains a list of strings; the actual use case is a wxPython drag-and-drop shell that I find I keep re-using over and over, so I decided to try to turn it into a general-purpose module for my own use.)

### example 1 begin

class Thing(object):
    def __init__(self):
        self.stuff = []
    def addstuff(self, text):
        self.add_the_stuff(text)
    def add_the_stuff(self, s1):
        self.stuff.append(s1)

A = Thing()
A.addstuff("ABCDEFG")
print A.stuff

### example 1 end

So far, this works as expected. addstuff invokes add_the_stuff; and the line "print A.stuff" prints out as ['ABCDEFG'], as expected.

Now, here's where I am getting befuddled, with the following additional lines:

### example, continued
def addlower(self, s2):
    self.stuff.append(s2.lower()) # add it as lower case

B = Thing()
B.add_the_stuff=addlower
B.addstuff("WXYZ")
print B.stuff
### end

My *intent* here is to patch the Thing object named B so that the B's add_the_stuff method is replaced with this additional addlower method that I define external to the object. My expectation would be that, just as add_the_stuff method was called with two arguments (self and the string), the patched-in addlower would also get called the same way.

What I *expect* is to see ['abcdefg'] printed.  What I get is:

Traceback (most recent call last):
  File "E:\Personal\py\DragDrop\toy.py", line 22, in <module>
    B.addstuff("WXYZ")
  File "E:\Personal\py\DragDrop\toy.py", line 7, in addstuff
    self.add_the_stuff(text)
TypeError: addlower() takes exactly 2 arguments (1 given)

I'm assuming I'm missing some fundamental concept.  What is it?
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