print odd numbers of lines from tekst WITHOUT space between lines

[Peter Otten]

TTaglo wrote:

> i = 1
> f = open ('rosalind_ini5(1).txt')
> for line in f.readlines():
>     if i % 2 == 0:
>         print line
>     i += 1
> 
> 
> How do i get output without breaks between the lines?

I'm late to the show, but here are a few unsolicited remarks to your code.

(1) The best way to open a file is

with open(filename) as f:
    # use the file
# at this point the file is closed without the need to invoke 
# f.close() explicitly

(2) The readlines() method reads the complete file into a list. This can 
become a problem if the file is large. It is better to iterate over the file 
directly:

for line in f:
    # use the line

(3) If you read the file into a list you can get all odd lines with

for odd_line in f.readlines()[1::2]:
   # use the odd line

(4) If you follow my advice from (2) and want to avoid the in-memory list 
there's an equivalent itertools.islice() function that you can use like 
this:

import itertools
for odd_line in itertools.islice(f, 1, None, 2):
    # use the odd line

(5) sys.stdout.write() was already mentioned, but there is also a 
sys.stdout.writelines() meathod which takes a sequence of strings. With that 
your code may become

import itertools
import sys

with open('rosalind_ini5(1).txt') as f:
    sys.stdout.writelines(itertools.islice(f, 1, None, 2))