Creating unique combinations from lists

[breal]

I have three lists... for instance

a = ['big', 'small', 'medium'];
b = ['old', 'new'];
c = ['blue', 'green'];

I want to take those and end up with all of the combinations they
create like the following lists
['big', 'old', 'blue']
['small', 'old', 'blue']
['medium', 'old', 'blue']
['big', 'old', 'green']
['small', 'old', 'green']
['medium', 'small', 'green']
['big', 'new', 'blue']
['small', 'new', 'blue']
['medium', 'new', 'blue']
['big', 'new', 'green']
['small', 'new', 'green']
['medium', 'new', 'green' ]

I could do nested for ... in loops, but was looking for a Pythonic way
to do this. Ideas?

[=?ISO-8859-1?Q?=22Martin_v=2E_L=F6wis=22?=]

The main emphasis was to show that there was a pattern unfolding that

should have been translated into more pythonic code than just
hard-coding nested loops.

Practicality beats purity. That you would solve a more general problem
in a more general way doesn't mean that you shouldn't solve the more
specific problem (combinations from three sets) in a specific,
easy-to-read way. Readability counts.

I find your solution (with nested generators) *very* unpythonic. It
is much more complicated than necessary to solve the problem at hand,
and it doesn't get Pythonic just by using the latest language features.
It may be a smart solution, but not a Pythonic one.

Regards,
Martin

P.S. To solve the general problem, I like

http://aspn.activestate.com/ASPN/Coo.../Recipe/496807

[Steven D'Aprano]

On Thu, 17 Jan 2008 10:44:51 -0600, Reedick, Andrew wrote:

>-----Original Message-----
From: Tim Chase [mailto:py****** ***@tim.thechas es.com] Sent: Thursday,
January 17, 2008 10:30 AM To: Reedick, Andrew
Cc: breal; py*********@pyt hon.org; ma****@v.loewis .de Subject: Re:
Creating unique combinations from lists

Yick...a nice demo of the power of eval, but definitely filed under the
"Hack" heading

You hurt my feeling. *sniffle* Given how late python
compiles/evaluates code blocks, I'm thinking that eval() is less hack
and more paradigm ..err.. pythonic. ;-)

I see your smiley, but even so, do you have any idea how many times eval
is used in the standard library? Not very often.

$ pwd
/usr/lib/python2.5
$ grep -r "eval(.*)" *.py | wc -l
20

Some of those twenty matches are false positives. I manually inspected
them, and by my count there are just ten actual uses of eval:

bdb.py: return eval(expr, globals, locals)
dumbdbm.py: key, pos_and_siz_pai r = eval(line)
gettext.py: return eval('lambda n: int(%s)' % plural)
gopherlib.py: _type_to_name_m ap[eval(name)] = name[2:]
mhlib.py: def do(s): print s; print eval(s)
os.py: eval(name)
pdb.py: x = eval(arg, {}, {})
rexec.py: return eval(code, m.__dict__)
rlcompleter.py: object = eval(expr, self.namespace)
warnings.py: cat = eval(category)
I haven't made any effort to determine how many of them are gaping great
big security holes.

--
Steven