Part 2 Of A Successful Outcome Regarding White-space Filling

So, my first question was answered correctly. For reference you can go here... How to fill the white-space with info while leaving the rest unchanged? In short, I needed this... PO

Solution 1:

As pointed out in the comments, keep a reference to the previous line:

with open('in.txt') as fin, open('out.txt', 'w') as fout:
    prev = None
    for i, line in enumerate(fin):
      if line.strip() != 'END_POLY' and prev:
        fout.write(prev)
      prev = line
      if not i % 10000:
        print('Processing line {}'.format(i))
    fout.write(line)

Solution 2:

Although not in python, these types of editing is quite straighforward if you use sed

sed 'N;s/.*\n\(END_POLY\)/\1/' file.txt

Basically what it does is that it uses N to read 2 lines at a time, if the second line contains the string END_POLY, it removes the first line, leaving only END_POLY

Solution 3:

if you don't want duplicated data, you can trasform the list into set, then into list (taking the @Jean-François Fabre code from the other question an little modific):

import itertools, collections

with open("file.txt") as f, open("fileout.txt","w") as fw:
    fw.writelines(itertools.chain.from_iterable([["BEGIN_POLYGON\n"]+list(collections.OrderedDict.fromkeys(v).keys())+["END_POLYGON\n"] for k,v in itertools.groupby(f,key = lambda l : bool(l.strip())) if k]))

as you can see, if you do:

print(list(collections.OrderedDict.fromkeys([1,1,1,1,1,1,2,2,2,2,5,3,3,3,3,3]).keys()))

it will be -> [1, 2, 5, 3] and yo preserve the order