[Tutor] Text Processing Query

[Spyros Charonis]

Hello Pythoners,

I am trying to extract certain fields from a file that whose text looks
like this:

COMPND   2 MOLECULE: POTASSIUM CHANNEL SUBFAMILY K MEMBER 4;

COMPND   3 CHAIN: A, B;

COMPND  10 MOL_ID: 2;

COMPND  11 MOLECULE: ANTIBODY FAB FRAGMENT LIGHT CHAIN;

COMPND  12 CHAIN: D, F;

COMPND  13 ENGINEERED: YES;

COMPND  14 MOL_ID: 3;

COMPND  15 MOLECULE: ANTIBODY FAB FRAGMENT HEAVY CHAIN;

COMPND  16 CHAIN: E, G;

I would like the chain IDs, but only those following the text heading
"ANTIBODY FAB FRAGMENT", i.e. I need to create a list with D,F,E,G  which
excludes A,B which have a non-antibody text heading. I am using the
following syntax:

with open(filename) as file:

    scanfile=file.readlines()

    for line in scanfile:

        if line[0:6]=='COMPND' and 'FAB FRAGMENT' in line: continue

        elif line[0:6]=='COMPND' and 'CHAIN' in line:

            print line

But this yields:

COMPND   3 CHAIN: A, B;

COMPND  12 CHAIN: D, F;

COMPND  16 CHAIN: E, G;

I would like to ignore the first line since A,B correspond to non-antibody
text headings, and instead want to extract only D,F & E,G whose text
headings are specified as antibody fragments.

Many thanks,
Spyros
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