Biopython ; pdb file parsing

Question

[fareehakanwal90]

How do I extract a specific residue from a pdb file though biopython? for example I have to extract 23,24th and 27th residue only. How do I do that?

Here is my code:

from Bio.PDB import *
from itertools import groupby
from operator import itemgetter
parser=PDBParser()
structure=parser.get_structure('X', '4wwt_loop_mcannotate.pdb')
faa=open('4wwt_loop_mcannotate.pd','w')
#fasta=[]
reslist=[]
structure=parser.get_structure('X' , '4wwt_loop_mcannotate.pdb')
for model in structure:
    for chain in model:
        for residue in chain:
            #few=residue.get_id[1]
            reslist.append(residue.get_id())
            faa.write(residue.get_resname().strip())
faa.close()
residuelist=[]
for items in reslist:
    for elemts in items:
        if elemts==' ':
            continue
        else:
            residuelist.append(elemts)
fraglist=[]
for k,g in groupby(enumerate(residuelist), lambda(i,x):i-x):
    fraglist.append(map(itemgetter(1),g))
print fraglist
myfrags=[]
myfragment=''
for ies in fraglist:
    for item in ies:   
        for model in structure:
            for chain in model:
                for residue in chain:
                    if item in residue.get_id():
                        myfragment+=residue.get_resname().strip()
                        myfragment+=str(item)
                        myfrags.append(myfragment)
                        myfragment=''
print myfrags

and this is the output I am getting

[[2724, 2725], [2741, 2742, 2743, 2744, 2745, 2746], [2792, 2793, 2794, 2795, 2796]]
['C2724', 'C2725', 'G2741', 'U2742', 'G2743', 'G2744', 'A2745', 'U2746', 'A2792', 'A2793', 'U2794', 'C2795', 'G2796']

while I want the output as set of fragments, like [CC,GUGGA, UAAUCG]

Please if someone could help

[venu]

Can you show your pdb file? Is it taken form Protein data bank?

[fareehakanwal90]

No it's generated by a tool. here it is: