xrange not adhering to start, stop, step

Question

My input file looks like:

6
*,b,*
a,*,*
*,*,c
foo,bar,baz
w,x,*,*
*,x,y,z
5
/w/x/y/z/
a/b/c
foo/
foo/bar/
foo/bar/baz/

When I use xrange, why does it not adhere to the start, stop, step method?

with open(sys.argv[1], 'r') as f:
  for _ in xrange(0, 7, 1):
    next(f)
  for listPatterns in f:
    print listPatterns.rstrip()

It outputs the text starting at line 7 when in actuality I want it to print line 1 through 7.

? Your loop skips the first 7 lines (there is no `print` indented in that loop). Nothing wrong with the `xrange()` — beroe, Nov 13 '13 at 17:43

score 4 · Accepted Answer · answered Nov 13 '13 at 17:44

4

The code you want is

with open(sys.argv[1], 'r') as f:
  for _ in xrange(0, 7, 1):
    print f.next().rstrip()

The first loop you have is advancing through the file.

answered Nov 13 '13 at 17:44

colcarroll

3,632
17
25

score 1 · Answer 2 · answered Nov 13 '13 at 17:48

For each item in the iterable (in this case xrange) you're calling next on the file-obj and ignoring the result - either do something with that result, or better yet, make it much clearer:

from itertools import islice
with open('file') as fin:
    for line in islice(fin, 7):
        # do something

score 0 · Answer 3 · answered Nov 13 '13 at 17:44

0

Er, well, because you told it to skip the first 7 lines? Solution: don't do that.

answered Nov 13 '13 at 17:44

kindall

178,883
35
278
309

score 0 · Answer 4 · answered Nov 13 '13 at 17:45

0

it isn't xrange.

you first loop through all of xrange.

then you exit the loop

then you have another loop, acting on the last element

answered Nov 13 '13 at 17:45

vish

1,046
9
26

score 0 · Answer 5 · answered Nov 13 '13 at 17:48

You can also iterate through the file, without using a proxy iterator

START_LINE = 0
STOP_LINE = 6
with open(sys.argv[1], 'r') as f:
   for i, line in enumerate(f.readlines()):
       if START_LINE <= i <= STOP_LINE:
           print line.rstrip()
       elif i > STOP_LINE: 
           break

xrange not adhering to start, stop, step

5 Answers5