尝试从列表中获取除头两个元素以外的其他内容时，Python给我一个错误

Question

I'm trying to extract some info out of a .gtf file, which is basically like a type of database where items are tab delimited(or so i'm told). I've written the following simple code to break up each line of the file into a list so each item in the list is one of the "columns" (and also print out the comment lines, but ignore that)

for line in file:
    if line.startswith('#'):
        print (line)
line = line.rstrip('\n')
field = line.split()

Pretty simple code, and when I put in a print(field) it prints out many lines like this one with varying data

['1', 'havana', 'exon', '7962767', '7962875', '.', '+', '.', 'gene_id', '"ENSG00000116288";', 'gene_version', '"12";', 'transcript_id', '"ENST00000497113";', 'transcript_version', '"1";', 'exon_number', '"1";', 'gene_name', '"PARK7";', 'gene_source', '"ensembl_havana";', 'gene_biotype', '"protein_coding";', 'transcript_name', '"PARK7-210";', 'transcript_source', '"havana";', 'transcript_biotype', '"processed_transcript";', 'exon_id', '"ENSE00001935602";', 'exon_version', '"1";', 'transcript_support_level', '"3";']

I figure it looks like a list right. So I go to test it with print()

print(field[0])
print(field[1])
print(field[-1])
print(field[-2])

and those give me this

1
havana
"5";
transcript_support_level

etc. So it looks like a list, and acts like a list, but the data I want is in the third column so I just change the code to field[2] and it gives me this

   print(field[2])
IndexError: list index out of range

I tried putting in different numbers but it's all the same error, and I just really can't figure out why it would let me pull up the first two and last two items in the list, but nothing else? I've tried a lot of things but i'm really just stumped as to what to do here. I can't continue with my code unless I'm able to reference the third column/item in these lists.

Answer 1

Well I did find a work-around for it with the following code

for line in file:
    if line.startswith('#'):
        print (line)
    line = line.rstrip('\n')
    field = line.split("\t")
    for item in field[2:3:1]:
        print(item)

It's pretty simple and I probably should have thought of it sooner, but it lets me print out all the items in the third column, so it works but I feel like I just wrote the same thing in different words. Still confused as to why it would only work in a limited fashion the other way though...