How to select every other line from a text file?

Chris Angelico rosuav at
Mon Oct 13 19:46:33 CEST 2014

On Tue, Oct 14, 2014 at 4:38 AM, Rff <rwang at> wrote:
> I have a text file. Now it is required to select every other line of that text to
>  generate a new text file. I have read through Python grammar, but still lack the
>  idea at the beginning of the task. Could you tell me some methods to get this?

There are a few ways of doing this. I'm guessing this is probably a
homework assignment, so I won't give you the code as-is, but here are
a few ideas:

1) Iterate over the file (line by line), alternating between writing
the line out and not writing the line out.
2) Read the file into a list of lines, then slice the list with a step
of 2, and write those lines out.
3) Iterate over the file, but also consume an extra line at the top or
bottom of the loop.
4) Read the entire file into a string, then abuse regular expressions
violently until they do what you want.

And there are other ways, too. Show us some code and we can help you
with it; but at the moment, this is fairly open-ended.


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