[Tutor] Working with lines from file and printing to another keeping sequential order

[Kent Johnson]

On Sat, Apr 25, 2009 at 2:11 PM, Dan Liang <danliang20 at gmail.com> wrote:
> Hi Bob and tutors,
>
> Thanks Bob for your response! currently I have the current code, but it does
> not work:
>
> ListLines= []
> for line in open('test.txt'):
>     line = line.rstrip()
>     ListLines.append(line)

This could be written with a list comprehension:
ListLines = [ line.rstrip() for line in open('test.txt') ]

>
> for i in range(len(ListLines)):
>
>     if ListLines[i].endswith("yes") and ListLines[i+1].endswith("no") and
> ListLines[i+1].endswith("no"):
>         print ListLines[i], ListLines[i+1], ListLines[i+2]
>     elif ListLines[i].endswith("yes") and ListLines[i+1].endswith("no"):
>         print ListLines[i], ListLines[i+1]
>         elif ListLines[i].endswith("yes"):
>         print ListLines[i]
>     elif ListLines[i].endswith("no"):
>         continue
>     else:
>         break

You only need to test for ListLines[i].endswith('yes') once. Then you
could use a loop to test for lines ending with 'no'.

for i in range(len(ListLines)):
  if not ListLines[i].endswith('yes'):
    continue
  for offset in (1, 2):
    if i+offset < len(ListLines) and ListLines[i+offset].endswith('no'):
      print ListLines[i+offset]

You could adapt the above for a variable number of 'no' lines with
something like
  for offset in range(1, maxNo+1):

> I get the following error:
> Traceback (most recent call last):
>   File "test.py", line 18, in <module>
>     if ListLines[i].endswith("yes") and ListLines[i+1].endswith("no") and
> ListLines[i+1].endswith("no"):
> IndexError: list index out of range

That is because you have a 'yes' line at the end of the file so the
check for 'no' tries to read past the end of ListLines. In my code the
test for i+offset < len(ListLines) will prevent that exception.

Kent