Random and fork

Newsgroups	comp.lang.python
Date	2013-02-06 08:28 -0800
Message-ID	<9efb072f-b671-45da-bc4e-ef224b2ffe76@googlegroups.com> (permalink)
Subject	Random and fork
From	Julien Le Goff <julien.legoff@gmail.com>

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Hi everyone,

Today I came accross a behaviour I did not expect in python (I am using 2.7). In my program, random.random() always seemed to return the same number; it turned out to be related to the fact that I was using os.fork.

See below a small program that illustrates this. It is easily fixed, but I'm interested in knowing why this happens. Can anybody give me a hint? Thanks!

import random
import os

for i in xrange(10):
    pid = os.fork()
    if pid == 0:
        # uncommenting this fixes the problem
        # random.seed(os.getpid())
        print random.random()
        os._exit(0)

os.wait()

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Random and fork Julien Le Goff <julien.legoff@gmail.com> - 2013-02-06 08:28 -0800
  Re: Random and fork Peter Otten <__peter__@web.de> - 2013-02-06 17:47 +0100
  Re: Random and fork Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-02-06 17:49 +0100
    Re: Random and fork Julien Le Goff <julien.legoff@gmail.com> - 2013-02-07 01:41 -0800
  Re: Random and fork Stephane Wirtel <stephane@wirtel.be> - 2013-02-07 14:29 +0100

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