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This bug is a major problem for us as well. This bug also
breaks the subprocess module. Try, for example:

subprocess.Popen(["ls"], close_fds=1, preexec_fn=lambda:
os.urandom(4))

I agree with lcaamano; the library should NOT cache a file
descriptor by default. Correctness and robustness is more
important than speed. 

Has anyone really been able to verify that the performance
with opening /dev/urandom each time is a problem? If it is,
we could add a new function to the os module that activates
the fd caching. If you have been calling this function, you
have indicated that you are aware of the problem and will
not close the cached fd. Legacy code will continue to function.