python: practice ,for i in range

list ,dict,tuple, or docentment all can use     for    in  loop> 

number=0

for i   in file:

    number+=1

   if i ==3:

        i=" ".join((i.strip,'word')

   print(i)

read article,cursor persent position. can using "seek( number)" work it

for in stance:

f.seek(30)

flush

from cache(computer temporary storage region, for a short time store area .main function is improve  pc productivity)

to disk (permanent storage area.)