Question

My input file is one sentence per line. Let’s say it looks like:

A
B
C
D
E
F

Desired output is:

::NewPage::
A
B
::NewPage::
C
D
::NewPage::
E
F

I know that I should be using a while loop but not sure how to?

Answer 1

You don’t need a while loop here – look at the grouper recipe in itertools.

def grouper(n, iterable, fillvalue=None):
    "Collect data into fixed-length chunks or blocks"
    # grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx"
    args = [iter(iterable)] * n
    return zip_longest(*args, fillvalue=fillvalue)

Note that you will need a slightly different version if you are using 2.x.

E.g:

items = ["A", "B", "C", "D", "E"]
for page in grouper(2, items):
    print("::NewPage::")
    for item in page:
        if item is not None:
            print(item)

Which produces:

::NewPage::
A
B
::NewPage::
C
D
::NewPage::
E

If you need None values, you can use a sentinel object.