Text file processing in python

Question

I have the following file:

1    real madrid,barcelona,chelsea,arsenal,cska
2    chelsea,arsenal,milan,napoli,juventus
5    bayern,dortmund,celtic,napoli
7    cska,psg,arsenal,atalanta
9    atletic bilbao,las palmas,milan,barcelona

and I want to produce a new file with this output (where I had the nodes, now I have every team and in the second column I have the nodes that has this team as attribute):

real madrid    1
barcelona    1,9
chelsea    1,2
arsenal    1,2,7
cska    1,7
milan    2,9
etc...

First of all i opened the file and I saved each column to a list:

file1 = open("myfile.txt","r")
lines1 = file1.readlines()
nodes1 = []
attrs1 = []


for x in lines1:
    x = x.strip()
    x = x.split('\t')
    nodes1.append(x[0])
    attrs1.append(x[1].split(','))

but now how can I check the attrs and nodes to produce the output file?

Answer 1

Better, create a dictionary when reading the file:

line_map = {}
for x in lines1:
    (row_no, teams) = x.strip().split("\t")
    for i in teams.split(","):
        if not i in line_map:
            line_map[i] = set()
        line_map[i].add(row_no)

Now line_map contains a mapping of the team name to a list of lines it is contained on. You can easily print that:

for (k, v) in line_map.items():
    print("%s: %s" % (k, ",".join(v)))

if I am not much mistaken...

Edit: append should have been add.