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Re: How can I speed up a script that iterates over a large range (600 billion)?

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On Tue, Jun 21, 2011 at 1:48 PM, John Salerno <johnjsal@gmail.com> wrote:
> Here is what I have so far. Initially the get_factors function just
> iterated over the entire range(2, n + 1), but since a number can't
> have a factor greater than half of itself, I tried to shorten the
> range by doing range(2, n //2), but that still leaves 300 billion
> numbers to go through.

Without giving you the answer, I will note that the range can be
further reduced by quite a lot (I'm talking orders of magnitude, not
just by half).

> def get_primes(number_list):
>    primes = number_list[:]
>
>    for n in number_list:
>        for x in range(2, n):
>            if n % x == 0:
>                primes.remove(n)
>                break
>
>    return primes

Also, primality testing and factorization are very similar problems,
and the same range optimization could be applied here as well.

Cheers,
Ian

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How can I speed up a script that iterates over a large range (600 billion)? John Salerno <johnjsal@gmail.com> - 2011-06-21 12:48 -0700
  Re: How can I speed up a script that iterates over a large range (600 billion)? Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-21 14:02 -0600
  Re: How can I speed up a script that iterates over a large range (600 billion)? Irmen de Jong <irmen@-NOSPAM-xs4all.nl> - 2011-06-21 22:10 +0200
    sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? Irmen de Jong <irmen@-NOSPAM-xs4all.nl> - 2011-06-21 22:22 +0200
      Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? John Salerno <johnjsal@gmail.com> - 2011-06-21 14:09 -0700
        Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? Irmen de Jong <irmen.NOSPAM@xs4all.nl> - 2011-06-21 23:39 +0200
        Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-21 15:41 -0600
          Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? John Salerno <johnjsal@gmail.com> - 2011-06-21 14:48 -0700
        Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? Vlastimil Brom <vlastimil.brom@gmail.com> - 2011-06-21 23:33 +0200
        Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? Paul Rubin <no.email@nospam.invalid> - 2011-06-21 17:05 -0700
          Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? John Salerno <johnjsal@gmail.com> - 2011-06-21 18:21 -0700
            Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? Paul Rubin <no.email@nospam.invalid> - 2011-06-21 19:09 -0700
              Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? John Salerno <johnjsal@gmail.com> - 2011-06-21 20:02 -0700
                Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? Irmen de Jong <irmen.NOSPAM@xs4all.nl> - 2011-06-22 19:46 +0200
            Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? MRAB <python@mrabarnett.plus.com> - 2011-06-22 03:10 +0100
            Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? Mel <mwilson@the-wire.com> - 2011-06-21 23:02 -0400
              Re: sorry, possibly too much info. was: Re: How can I speed up a script that iterates over a large range (600 billion)? John Salerno <johnjsal@gmail.com> - 2011-06-21 20:41 -0700
  Re: How can I speed up a script that iterates over a large range (600 billion)? Mel <mwilson@the-wire.com> - 2011-06-21 16:19 -0400
    Re: How can I speed up a script that iterates over a large range (600 billion)? Tim Roberts <timr@probo.com> - 2011-06-22 23:21 -0700
  Re: How can I speed up a script that iterates over a large range (600 billion)? MRAB <python@mrabarnett.plus.com> - 2011-06-21 21:26 +0100
  Re: How can I speed up a script that iterates over a large range (600 billion)? Terry Reedy <tjreedy@udel.edu> - 2011-06-21 19:30 -0400
    Re: How can I speed up a script that iterates over a large range (600 billion)? Paul Rubin <no.email@nospam.invalid> - 2011-06-21 17:00 -0700
      Re: How can I speed up a script that iterates over a large range (600 billion)? Terry Reedy <tjreedy@udel.edu> - 2011-06-22 00:18 -0400
        Re: How can I speed up a script that iterates over a large range (600 billion)? Paul Rubin <no.email@nospam.invalid> - 2011-06-21 22:32 -0700
          Re: How can I speed up a script that iterates over a large range (600 billion)? Terry Reedy <tjreedy@udel.edu> - 2011-06-22 18:46 -0400
  Re: How can I speed up a script that iterates over a large range (600 billion)? Benjamin Kaplan <benjamin.kaplan@case.edu> - 2011-06-21 20:07 -0700
  Re: How can I speed up a script that iterates over a large range (600 billion)? Chris Torek <nospam@torek.net> - 2011-06-22 05:58 +0000
    Re: How can I speed up a script that iterates over a large range (600 billion)? Paul Rubin <no.email@nospam.invalid> - 2011-06-21 23:23 -0700
      Re: How can I speed up a script that iterates over a large range (600 billion)? Slaunger <slaunger@gmail.com> - 2011-06-23 02:52 -0700
    Re: How can I speed up a script that iterates over a large range (600 billion)? Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-22 01:16 -0600
    Re: How can I speed up a script that iterates over a large range (600 billion)? Anny Mous <b1540457@tyldd.com> - 2011-06-22 22:01 +1000
      Re: How can I speed up a script that iterates over a large range (600 billion)? Chris Angelico <rosuav@gmail.com> - 2011-06-22 22:28 +1000
      Re: How can I speed up a script that iterates over a large range (600 billion)? Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-22 09:52 -0600
    Re: How can I speed up a script that iterates over a large range (600 billion)? MRAB <python@mrabarnett.plus.com> - 2011-06-22 16:33 +0100

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