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Re: How to read from a file to an arbitrary delimiter efficiently?

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On 29 February 2016 at 07:28, Oscar Benjamin <oscar.j.benjamin@gmail.com>
wrote:

> On 25 February 2016 at 06:50, Steven D'Aprano
> <steve+comp.lang.python@pearwood.info> wrote:
> >
> > I have a need to read to an arbitrary delimiter, which might be any of a
> > (small) set of characters. For the sake of the exercise, lets say it is
> > either ! or ? (for example).
> >
> > I want to read from files reasonably efficiently. I don't mind if there
> is a
> > little overhead, but my first attempt is 100 times slower than the
> built-in
> > "read to the end of the line" method.
>
> You can get something much faster using mmap and searching for a
> single delimiter:
>
> My timing makes that ~7x slower than iterating over the lines of the
> file but still around 100x faster than reading individual characters.
> I'm not sure how to generalise it to looking for multiple delimiters
> without dropping back to reading individual characters though.
>

You can use an mmapped file as the input for regular expressions. May or
may not be particularly efficient.

Otherwise, if reading from a file I think read a chunk, and seek() back to
the delimiter is probably going to be most efficient whilst leaving the
file position just after the delimiter.

If reading from a stream, I think Chris' read a chunk and maintain an
internal buffer, and don't give access to the underlying stream.

Tim Delaney

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Thread

How to read from a file to an arbitrary delimiter efficiently? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-02-25 17:50 +1100
  Re: How to read from a file to an arbitrary delimiter efficiently? Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2016-02-25 08:37 +0100
    Re: How to read from a file to an arbitrary delimiter efficiently? Steven D'Aprano <steve@pearwood.info> - 2016-02-27 21:40 +1100
      Re: How to read from a file to an arbitrary delimiter efficiently? Dan Sommers <dan@tombstonezero.net> - 2016-02-27 14:40 +0000
      Re: How to read from a file to an arbitrary delimiter efficiently? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-02-27 12:03 -0500
        Re: How to read from a file to an arbitrary delimiter efficiently? Marko Rauhamaa <marko@pacujo.net> - 2016-02-27 19:47 +0200
  Re: How to read from a file to an arbitrary delimiter efficiently? Chris Angelico <rosuav@gmail.com> - 2016-02-25 18:30 +1100
    Re: How to read from a file to an arbitrary delimiter efficiently? Steven D'Aprano <steve@pearwood.info> - 2016-02-27 20:49 +1100
      Re: How to read from a file to an arbitrary delimiter efficiently? Chris Angelico <rosuav@gmail.com> - 2016-02-27 23:17 +1100
      Re: How to read from a file to an arbitrary delimiter efficiently? Chris Angelico <rosuav@gmail.com> - 2016-02-27 23:18 +1100
      Re: How to read from a file to an arbitrary delimiter efficiently? Serhiy Storchaka <storchaka@gmail.com> - 2016-02-27 17:23 +0200
  Re: How to read from a file to an arbitrary delimiter efficiently? Paul Rubin <no.email@nospam.invalid> - 2016-02-24 23:48 -0800
    Re: How to read from a file to an arbitrary delimiter efficiently? wxjmfauth@gmail.com - 2016-02-25 06:37 -0800
    Re: How to read from a file to an arbitrary delimiter efficiently? wxjmfauth@gmail.com - 2016-02-25 06:38 -0800
  Re: How to read from a file to an arbitrary delimiter efficiently? BartC <bc@freeuk.com> - 2016-02-27 16:35 +0000
    Re: How to read from a file to an arbitrary delimiter efficiently? BartC <bc@freeuk.com> - 2016-02-27 20:03 +0000
      Re: How to read from a file to an arbitrary delimiter efficiently? BartC <bc@freeuk.com> - 2016-02-27 20:28 +0000
  Re: How to read from a file to an arbitrary delimiter efficiently? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-02-28 20:28 +0000
  Re: How to read from a file to an arbitrary delimiter efficiently? Tim Delaney <timothy.c.delaney@gmail.com> - 2016-02-29 08:00 +1100

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