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Re: Random string of digits?

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On Mon, Dec 26, 2011 at 12:30 AM, Roy Smith <roy@panix.com> wrote:
> I want to create a string of 20 random digits (I'm OK with leading
> zeros).  The best I came up with is:
>
> ''.join(str(random.randint(0, 9)) for i in range(20))
>
> Is there something better?

The simple option is:
random.randint(0,99999999999999999999)
or
"%020d"%random.randint(0,99999999999999999999)
(the latter gives you a string, padded with leading zeroes). But I'm
assuming that you discarded that option due to lack of entropy (ie you
can't trust randint() over that huge a range).

The way I'd do it would be in chunks. The simple option is one chunk;
your original technique is twenty. We can go somewhere in between.
First thing to do though: ascertain how far randint() is properly
random. The Python 2 docs [1] say that the underlying random()
function uses 53-bit floats, so you can probably rely on about that
much randomness; for argument's sake, let's say it's safe for up to
10,000 but no further (although 53 bits give you about 15 decimal
digits).

''.join('%04d'%random.randint(0,9999) for i in range(5))

For your actual task, I'd be inclined to take ten digits, twice, and
not bother with join():

'%010d%010d'%(random.randint(0,9999999999),random.randint(0,9999999999))

Looks a little ugly, but it works! And only two random number calls
(which can be expensive).

ChrisA

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Thread

Random string of digits? Roy Smith <roy@panix.com> - 2011-12-25 08:30 -0500
  Re: Random string of digits? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-25 13:48 +0000
    Re: Random string of digits? Chris Angelico <rosuav@gmail.com> - 2011-12-26 00:54 +1100
      Re: Random string of digits? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-25 15:46 +0000
        Re: Random string of digits? Chris Angelico <rosuav@gmail.com> - 2011-12-26 03:11 +1100
          Re: Random string of digits? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-25 17:18 +0000
            Re: Random string of digits? Roy Smith <roy@panix.com> - 2011-12-25 12:41 -0500
              Re: Random string of digits? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-25 11:50 -0800
              Re: Random string of digits? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-26 03:00 +0000
                Re: Random string of digits? Chris Angelico <rosuav@gmail.com> - 2011-12-26 14:43 +1100
                Re: Random string of digits? Roy Smith <roy@panix.com> - 2011-12-25 23:17 -0500
                Re: Random string of digits? Chris Angelico <rosuav@gmail.com> - 2011-12-26 15:26 +1100
    Re: Random string of digits? Serhiy Storchaka <storchaka@gmail.com> - 2011-12-25 19:32 +0200
  Re: Random string of digits? Chris Angelico <rosuav@gmail.com> - 2011-12-26 00:50 +1100
    Re: Random string of digits? Roy Smith <roy@panix.com> - 2011-12-25 09:21 -0500
      Re: Random string of digits? Chris Angelico <rosuav@gmail.com> - 2011-12-26 01:51 +1100
        Re: Random string of digits? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-25 15:27 +0000
  Re: Random string of digits? Chris Angelico <rosuav@gmail.com> - 2011-12-26 00:51 +1100
  Re: Random string of digits? Peter Otten <__peter__@web.de> - 2011-12-25 16:21 +0100

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