Generating the byte representation of a UUID object can be a little faster by using binascii's unhexlify on the hex value of the UUID object. In my testing, I saw about a 5.5x speed increase with the attached changes. 

Here are a set of benchmarks that I ran, which are inspired by Wang Chun's benchmarks on http://bugs.python.org/issue5885:

https://gist.github.com/kevinlondon/d3bb32d5a784f78731fa

My times:

kevin$ python uuid_benchmark.py 100000
Original Average: 8.049 microseconds
Updated Average: 1.447 microseconds
 
I re-ran all of the tests with the patched uuid module and they passed. Here's my patchcheck output as well:

kevin$ make patchcheck
./python.exe ./Tools/scripts/patchcheck.py
Getting the list of files that have been added/changed ... 1 file
Fixing whitespace ... 0 files
Fixing C file whitespace ... 0 files
Fixing docs whitespace ... 0 files
Docs modified ... NO
Misc/ACKS updated ... NO
Misc/NEWS updated ... NO
configure regenerated ... not needed
pyconfig.h.in regenerated ... not needed

Thanks!

`self.int.to_bytes(16, byteorder='big')` looks to be even faster (about 3x on my machine)

What I said only applies to the Python3 version of this patch.

Thanks for submitting this.

I also like the way the patch cleans-up the code.

If such changes are acceptable, here is a part of my large patch fo modernizing stdlib sources.

Some microbenchmarks:

$ ./python -m timeit -s "from uuid import NAMESPACE_DNS as u" -- "u.bytes"
$ ./python -m timeit -s "from uuid import NAMESPACE_DNS as u" -- "u.bytes_le"
$ ./python -m timeit -s "from uuid import UUID" -- "UUID(bytes_le=b'abcdefghijklmnop')"

Before patch:
10000 loops, best of 3: 66.9 usec per loop
10000 loops, best of 3: 102 usec per loop
10000 loops, best of 3: 65.2 usec per loop

After patch:
100000 loops, best of 3: 3.98 usec per loop
100000 loops, best of 3: 10.8 usec per loop
10000 loops, best of 3: 32.1 usec per loop

Just noticed that this patch also fixes a bug. When os.popen() fails in _ipconfig_getnode(), pipe is not set, and then NameError is raised in the finally branch.

Alex, Raymond, could you please make a review of my patch?

Patch looks good to me.

New changeset f7b5038d3102 by Serhiy Storchaka in branch 'default':
Issue #22131: Modernized the code of the uuid module.
http://hg.python.org/cpython/rev/f7b5038d3102

New changeset d8c6b15a2ae3 by Serhiy Storchaka in branch '2.7':
Issue #22131: Fixed a bug in handling an error occured during reading from
http://hg.python.org/cpython/rev/d8c6b15a2ae3

New changeset 8a61a287776d by Serhiy Storchaka in branch '3.4':
Issue #22131: Fixed a bug in handling an error occured during reading from
http://hg.python.org/cpython/rev/8a61a287776d

Thank you Alex.