[Tutor] Overriding a method in a class

[Terry Carroll]

On Fri, 13 May 2011, Terry Carroll wrote:

> For my specific case, I'm going to go with a Plan B of using callbacks; and 
> provide default unbound callbacks present in the module, but not defined in 
> the class itself.

Here's a callback-with-default approach, which works:

### Thing.py ############
def add_the_stuff(obj, s1):
     obj.stuff.append(s1)

class Thing(object):
     def __init__(self, callback=add_the_stuff):
         self.stuff = []
         self.cb=callback
     def addstuff(self, text):
         self.cb(self, text)
#########################

##### toy2.py ###########
import Thing

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

def addlower(obj, s2):
     obj.stuff.append(s2.lower())

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

Which produces, as expected:

>toy2.py
['ABCDEFG']
['wxyz']

But still...

> But I'd still like to have a better understanding of how the call gets 
> transmuted from a two-argument call to a one-argument call based upon the 
> target.