[Tutor] Help on best way to check resence of item inside list

[Steven D'Aprano]

On Tue, May 27, 2014 at 10:05:30AM +0200, jarod_v6 at libero.it wrote:
[...]
> with open("file.in") as p:
> mit = []

You have lost the indentation, which makes this code incorrect.

But the rest of the code is too complicated.

> for i in p:
>    lines =i.strip("\n").split("\t")
>    if  (lines[0] in clubA:
>               G =lines[-1] +["clubA"]
>    else:
>            G = lines[-1] +["no"]  
> mit.append(G)
> 
> for i in mit:
>    if i.strip("\n").split("\t")[0] in clubB:
>          G =lines[-1] +["clubB"]
>    else:
>            G = lines[-1] +["no"]  
>   finale.append(G)

Look at the result you want to get:

> mary  clubA clubB
> luke clubA
> luigi  no

That suggests to me that the best data structure is a dict with sets:

{'mary': set(['clubA', 'clubB']),
 'luke': set(['clubA']),
 'luigi': set(),
 }


Something like this should work:

names = {}
with open("file.in") as p:
    # This assumes the data file is one name per line.
    for line in p:
        name = line.strip()
        s = names.get(name, set())  # If name not in the names, 
                                    # return an empty set.
        if name in clubA:
            s.add("clubA")
        if name in clubB:
            s.add("clubB")
        names[name] = s

print(names)


And I think that should work.


-- 
Steven