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

[Peter Otten]

jarod_v6 at libero.it wrote:

> Dear All
> 
> clubA= ["mary","luke","amyr","marco","franco","lucia", "sally","genevra","
> electra"]
> clubB= ["mary","rebecca","jane","jessica","judit","sharon","lucia",
> "sally"," Castiel","Sam"]
> 
> I have a list of names that I would to annotate  in function of presence
> in different clubs:
> 
> my input files is a long file where I have this :
> 
> mary
> luke
> luigi
> jane
> jessica
> rebecca
> luis
> ################################################à
> 
> with open("file.in") as p:
> mit = []
> 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)
> ###############################################################
> I just wonder if is appropriate to use a loops to check if is present the
> value on a list. Is it the right way? I can use a dictionary because I
> have many repeated names.

You mean you have people who are members in more than one club? You can 
still use a dictionary if you make the value a list:

# untested code!

membership = {}

club = "club_of_people_who_are_not_in_any_club"
members = ["Erwin", "Kurt", "Groucho"]

for name in members:
    # can be simplified with dict.setdefault() or collections.defaultdict
    if name in membership:
        membership[name].append(club)
    else:
        membership[name] = [club]

Put that in a loop over (club, members) pairs, and you'll end up with a dict 
that maps name --> list_of_clubs.

Then iterate over the lines in the file:

with open("file.in") as source:
    for line in source:
        name = line.strip()
        if name in membership:
            print(name, *membership[name])
        else:
            print(name, "no")


> 
> In the end I wan to have
> 
> 
> mary  clubA clubB
> luke clubA
> luigi  no
> Thanks in advance for any help
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