[Tutor] extracting lists from lists of lists

[nik]

Kent Johnson wrote:

> I still don't understand why you can't use a simple class for this. 
> You can pass around instances of the class instead of tuples. You can 
> make lists or sets of class instances when you need more than one.
>
> Or if you decide to use a dict, you can pass that directly to clients 
> instead of making it into a tuple.
>
> Can you give an example of how you will use the tuples?
>
> Finally, you might be interested in some recipes in the online Python 
> Cookbook (http://aspn.activestate.com/ASPN/Cookbook/Python) for making 
> tuples with named members. They are immutable though, I think you said 
> you want users to be able to change the values.
>
> Kent
>

The tuples are for the kinterbasDB commands, like;

newPeople = (
    ('Lebed'       , 53),
    ('Zhirinovsky' , 57),
  )

for person in newPeople:
    cur.execute("insert into people (name_last, age) values (?, ?)", person)

That's the only place I need a tuple from my data structure, I have no 
other need to pass a tuple anywhere. My (C++) application continually 
creates the data structures which ends up in a list in a python module. 
The items in the list can then pass through various actions like values 
getting changed (mapping or mathmatical operations), database entry and 
manipulation, or even sent through a socket to somewhere else.
All the actions are in various python scripts which I'm allowing my 
users to edit freely (since they all have different requirements). I'd 
like to keep their life as simple as possible, and at the heart of that 
is this data structure.

Maybe I'm thinking too hard about it, and the original

class myData:
   name = ""
   age = ""
   gender = ""

was actually the simplest and clearest. I was concerned that a user 
would delete some of the items, causing problems later in the system. 
Also possibly I'm hung up on the idea of member variables in C++?

nik

> At 03:45 PM 9/14/2004 +0200, nik wrote:
>
>> Kent Johnson wrote:
>>
>>> At 12:52 PM 9/14/2004 +0200, nik wrote:
>>>
>>>> hi,
>>>>
>>>> I have a class which is just a holder for a data structure, and for 
>>>> some reason I've decided to hold the data in the following form;
>>>>
>>>> class myData:
>>>>    data = [  ["name", ""], ["age", ""], ["gender", ""] ]
>>>>
>>>> I'm not totally sure it's the best way, but it strikes me as 
>>>> something that can be easily manipulated into maps etc. I had 
>>>> started out with
>>>> class myData:
>>>>    name = ""
>>>>    age = ""
>>>>    gender = ""
>>>>
>>>> but I found that I had to put most of those items into lists to do 
>>>> anything with them.
>>>
>>>
>>>
>>> What kinds of things are you doing that you need these values in a 
>>> list? It sounds like maybe you are trying to pull the data out of 
>>> the class to pass to another function, but maybe it would be better 
>>> to pass the class itself around? Or maybe you should get rid of the 
>>> class entirely and just use a dictionary.
>>
>>
>> I'm thinking in terms of a C struct -  it's a handy parcel to move a 
>> set of data around, and quite likely there'll be stacks of sets. 
>> There's no extra functionality required from the set, and I'm not 
>> planning on deriving any other classes from this one. The dictionary 
>> seems a very good idea, but I think I still need to put it into a 
>> class since I'll have multiple instances of it - is that right? or 
>> can I do the equivalent of a typedef?
>
>
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