[Python-ideas] Add peekline(), peeklines(n) and optional maxlines argument to readlines()

[Eli Bendersky]

On Fri, Sep 30, 2011 at 13:28, Nick Coghlan <ncoghlan at gmail.com> wrote:
>
> On Fri, Sep 30, 2011 at 5:42 AM, Giampaolo Rodolà <g.rodola at gmail.com> wrote:
> > ...or 2 in case you're not at the beginning of the file.
> > before = f.tell()
> > f.peeklines(10)
> > f.seek(before)
>
> A context manager to handle the tell()/seek() may be an interesting
> and more general purpose idea:
>
>    # In the io module
>    class _TellSeek:
>        def __init__(self, f):
>            self._f = f
>        def __enter__(self):
>            self._position = self._f.tell()
>        def __exit__(self, *args):
>            self._f.seek(self._position)
>
>    def restore_position(f):
>        return _TellSeek(f)
>
>    # Usage
>    with io.restore_position(f):
>        for i, line in enumerate(f, 1):
>            # Do stuff
>            if i == 10:
>                break
>         else:
>            # Oops, didn't get as many lines as we wanted

This is useful, and made simpler by contextlib.contextmanager.
Actually I just posted this snipped on G+ a couple of weeks ago, since
I found it very useful for some stream-massaging code I was writing.
And yes, it only makes sense for seekable streams, of course.

So I'm -1 on the peeklines request, since it's easily implemented by
other means.

Eli