Pythonic method to sum all the odd-numbered lines in a file

Question

I\'m learning Python for a programming placement test I have to take for grad school, and this is literally the first little script I threw together to get a feel for it. My bac

Answer 1

I'm not sure how pythonic people may find this, but I find that zip, map, and reduce to be a pretty handy way to do this in a compact way. However, it can be a bit obfuscated.

with open("test.txt") as fd:                                                                                                           
   lines = [map(int, s.strip().split()) for s in fd.readlines()]                                                                      
   print "\n".join("Sample Size: %d \t Results: %d"%tuple(map(sum,(d[0],d[1])))                                                       
                   for d in zip(lines, lines[1:], range(len(lines)))                                                                  
                   if d[2] % 2 == 0)        

Answer 2

How about something like this, fairly Pythonic imho:

with open('test.txt') as fh:
    for i, line in enumerate(fh):
        if i % 2:
            nums = map(int, line.split())
            print 'Sample size: %d, Results: %d' % (len(nums), sum(nums))
        elif line == '0':
            print 'End of experiment'

Answer 3

You could do:

with open("test_file1.txt", "r") as inf:
    lines = inf.readlines()
    for l in lines[1::2]:  # read only alternating lines
        numList = map(int, line.split())
        print "Sample size:", len(numList), "Results:", sum(numList)

Answer 4

Use the file as an iterator, then use iterators.islice() to get every second line:

from itertools import islice

with open("test_file1.txt", "r") as f:
   for line in islice(f, 1, None, 2):
       nums = [int(n) for n in line.split()]
       print 'Sample size: {}  Results: {}'.format(len(nums), sum(nums))

islice(f, 1, None, 2) skips the first line (start=1), then iterates over all lines (stop=None) returning every second line (step=2).

This'll work with whatever filesize you throw at it; it won't need any more memory than required by the internal iterator buffer.

Output for your test file:

Sample size: 3  Results: 46
Sample size: 5  Results: 214
Sample size: 4  Results: 86
Sample size: 2  Results: 102