python - how to retrieve string from a large file -

i have written code in "ids.txt" tab deliminated text file contains id in manner given below in first column represent id second starting index , third column ending index.

ids.txt------- 

"complete.txt"

the script have write given bellow retrieve string fragment according "ids.txt" it's not working please changes should make correct code

with open("\users\zebrafish\desktop\ids.txt") f: # input text     line in f:         c = line.split("\t")                           i, x in enumerate(c):                #passing values  start , end variables              if == 1:                start = x             elif == 2:                 end =  x             elif == 0:                  gene_name = x         infile = open("/users/zebrafish/desktop/complete.txt")  #file large string data          seq in infile:             seqnew = seq.split("\t")                       # data single line          retrived = seqnew[int(start):int(end)]             #retrieve  fragment          print retrived 

i don't know why splitting on \t in complete.txt file, here code optimized:

ids = {} open('/users/zebrafish/desktop/ashish/ids.txt') f:     line in f:        if len(line.strip()):            # makes sure skip blank lines            id,start,end = line.split('\t')            ids[id] = (int(start),int(end))  # here, assume `complete.txt` file 1 long line. open('/users/zebrafish/desktop/ashish/complete.txt') f:     sequence = f.readline()  # each id, fetch sequence "chunk: id,value in ids.iteritems():     start, end = value     print('{} {}'.format(id,sequence[start-1:end]))