python newbie - where is my if/else wrong?

Complete beginner so I'm sorry if this is obvious!

I have a file which is name | +/- or IG_name | 0 in a long list like so -

S1      +
IG_1    0
S2      -
IG_S3   0
S3      +
S4      -
dnaA    +
IG_dnaA 0

Everything which starts with IG_ has a corresponding name. I want to add the + or - to the IG_name. e.g. IG_S3 is + like S3 is.

The information is gene names and strand information, IG = intergenic region. Basically I want to know which strand the intergenic region is on.

What I think I want:

open file
for every line, if the line starts with IG_*
    find the line with *
    print("IG_" and the line it found)
else 
    print line

What I have:

with open(sys.argv[2]) as geneInfo:
    with open(sys.argv[1]) as origin:
            for line in origin:
                    if line.startswith("IG_"):
                            name = line.split("_")[1]
                            nname = name[:-3]
                            for newline in geneInfo:
                                    if re.match(nname, newline):
                                            print("IG_"+newline)
                    else:
                            print(line)

where origin is the mixed list and geneInfo has only the names not IG_names.

With this code I end up with a list containing only the else statements.

S1  +

S2  -

S3  +

S4  -

dnaA    +

My problem is that I don't know what is wrong to search so I can (attempt) to fix it!