Expand IP ranges into a .txt file

ipRange.py

from sys import version
if int(version[0])<3:
    range=xrange
filename=input('File name(.txt): ')+'.txt'

with open(filename,'w') as file:
    while True:
        try:
            ipstart,ipend=[i.split('.') for i in input('IP range(split by -): ').split('-')]
            ipstart=[int(i) for i in ipstart]
            ipend=[int(i) for i in ipend]
        except ValueError:
            print('[ValueError]Wrong input. Please retry.')
            continue

        bok=False
        cok=False
        doc=False

        try:
            for a in range(ipstart[0],ipend[0]+1):
                bok=(ipstart[0]==ipend[0])
                for b in range(ipstart[1],ipend[1]+1 if bok else 256):
                    cok=((ipstart[1]==ipend[1]) and bok)
                    for c in range(ipstart[2],ipend[2]+1 if cok else 256):
                        dok=((ipstart[2]==ipend[2]) and cok)
                        for d in range(ipend(3)+1 if dok else 256):
                            file.write(str(a)+'.'+str(b)+'.'+str(c)+'.'+str(d)+'\n')
        except IndexError:
            print('[IndexError]Wrong input. Please retry.')
            continue
        print('Finished')