[Tutor] Lists on the fly?

[Luke Paireepinart]

[snip]
> # Get Levels List 
>     for Element in Elements:
>         Lev_List['Level_%i' % (Element['Level'])] = []
>
>     # Append Element to corresponding Level
>     for Element in Elements:
>         Lev_List['Level_%i' % (Element['Level'])].append(Element['Name'])
[snip snip]
> Probably the first loop is a little redundant, but performance is not 
> one of my concerns now, but in the future the project will not be 
> composed by a handful of spaces, probably by hundreds or more.
>   
I think a better way to do this is to check if 'Level_%i' is in your 
dictionary already.
so the loop becomes

Lev_List = {}
for Element in Elements:
    keystr = 'Level_%i' % Element['Level']
    if not Lev_List.has_key(keystr):
       Lev_List[keystr] = []
    Lev_List[keystr].append(Element['Name'])

And of course you can go the EAFP (easier to ask forgiveness than 
permission)
route and use a try/accept block

Lev_List = {}
for Element in Elements:
    keystr = 'Level_%i' % Element['Level']
    try:
       Lev_List[keystr].append(Element['Name'])
    except KeyError:
       Lev_List[keystr] = [Element['Name']]

I suspect the try/accept would be the fastest,
but you'd have to timeit to be sure, of course.
      
HTH,
-Luke