import re
myvar = False
myfile = open('extract','w')

with open('input.txt') as f:
    for line in f:
        if re.search(r'index1', line):
            myvar = True
            myfile.write(line)

        elif re.search(r'index2', line):
            myvar = False
            break

        elif myvar == True:
            myfile.write(line)
            continue

myfile.close
f.close