addvalue, how do i implement the code?

[Remco Gerlich]

Shaun wrote in comp.lang.python:
> 
> right lads heres what im trying todo:
> i make an empty list, (start=[])
> what i want to do is then add a name value pair say...('shaun',20)
> to the empty list,
> ive got a feeling the code looks somthing like what below but im not sure
> how to implement it can any of yous help me out on that one?
> Shaun
> 
> >>> class addv:
>     def add(self,x,y):
>         print'does not print'
>     def __init__(self,start=[]):
>         self.data=start
>     def __add__(self,other):
>         return addv(self.data, other)
> 
> >>> addv
> <class __console__.addv at 10486e0>
> >>> x=addv.add
> >>> x
> <unbound method addv.add>
> >>> x(3,4)
> Traceback (innermost last):
>   File "<pyshell#4>", line 1, in ?
>     x(3,4)
> TypeError: unbound method must be called with class instance 1st argument
> >>>

A few comments come to mind:

- You put these functions in a class, but it seems you only need one such
list. A class may not be necessary.

- To use a class, you have to make an instance of the class: inst = addv().
You can then call inst.add(name, value) to it.

- You define __add__, which is used to add ('+') instances to other instances.
It doesn't look like it does what you think it does.

- You use the empty list as default in the __init__ def, this is a little
trap: all instances will share the same list, probably not what you want.

- A dictionary would probably be the best place to store (name, value)
pairs, since you can do lookups on names quickly.


An improved class implementation looks like this:

class addv:
   def __init__(self):
      self.data = []
   def add(self, name, value):
      self.data.append((name, value))

inst = addv()
inst.add('shaun', 20)
print inst.data

With functions that would simply become:

data = []
def add(name, value):
   data.append((name, value))
   
add('shaun', 20)
print data

With a dictionary:

data = {}
def add(name, value):
   data[name] = value
   
add('shaun', 20)
print data
print data['shaun']
print data.items()

-- 
Remco Gerlich,  scarblac at pino.selwerd.nl

   This is no way to be
     Man ought to be free      -- Ted Bundy
       That man should be me