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Re: performance of script to write very long lines of random chars

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On Thu, Apr 11, 2013 at 3:33 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> I was originally going to write that using the base64 module would
> introduce bias into the random strings, but after a little investigation,
> I don't think it does.

Assuming that os.urandom() returns bytes with perfectly fair
distribution (exactly equal chance of any value 00-FF - it probably
does, or close to it), and assuming that you work with exact multiples
of 3 bytes and 4 output characters, base64 will give you perfectly
fair distribution of result characters. You take three bytes (24 bits)
and turn them into four characters (6 bits per character, = 24 bits).
You might see some bias if you use less than a full set of four output
characters, though; I haven't dug into the details to check that.

ChrisA

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performance of script to write very long lines of random chars gry <georgeryoung@gmail.com> - 2013-04-10 18:21 -0700
  Re: performance of script to write very long lines of random chars Chris Angelico <rosuav@gmail.com> - 2013-04-11 11:45 +1000
    Re: performance of script to write very long lines of random chars Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-11 05:33 +0000
      Re: performance of script to write very long lines of random chars Chris Angelico <rosuav@gmail.com> - 2013-04-11 15:53 +1000
  Re: performance of script to write very long lines of random chars Michael Torrie <torriem@gmail.com> - 2013-04-10 19:52 -0600
    Re: performance of script to write very long lines of random chars gry <georgeryoung@gmail.com> - 2013-04-10 19:40 -0700
      Re: performance of script to write very long lines of random chars Chris Angelico <rosuav@gmail.com> - 2013-04-11 13:14 +1000
  Re: performance of script to write very long lines of random chars MRAB <python@mrabarnett.plus.com> - 2013-04-11 04:09 +0100
  Re: performance of script to write very long lines of random chars Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-11 07:47 +0000
    Re: performance of script to write very long lines of random chars Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-11 10:47 +0100
      Re: performance of script to write very long lines of random chars Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-11 10:50 +0000
        Re: performance of script to write very long lines of random chars Robert Kern <robert.kern@gmail.com> - 2013-04-11 16:49 +0530
        Re: performance of script to write very long lines of random chars Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-11 13:05 +0100
        Re: performance of script to write very long lines of random chars Robert Kern <robert.kern@gmail.com> - 2013-04-11 19:06 +0530
        Re: performance of script to write very long lines of random chars Chris Angelico <rosuav@gmail.com> - 2013-04-11 23:56 +1000
  Re: performance of script to write very long lines of random chars Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-11 10:47 +0100

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