You might then be interested in the following related discussions from last year wherein I proposed something extremely similar:
[Python-ideas] proto-PEP: Fixing Non-constant Default Arguments http://mail.python.org/pipermail/python-ideas/2007-January/000121.html [Python-3000] pre-PEP: Default Argument Expressions http://mail.python.org/pipermail/python-3000/2007-February/005712.html The proposal was rejected by the BDFL (for being too magical) before it had become a full-fledged PEP. - Chris On Tue, Aug 26, 2008 at 8:21 PM, Sam Bishop <[EMAIL PROTECTED]> wrote: > Hi, all. > > I know that Python 3.0 is quite a ways along, but I'd like to make two > small suggestions with regards to how the language works. (I would > have spoken up earlier, except that I'm very new to Python.) > > I've talked to a few of my co-workers who are also new to Python, and > we've all been surprised at the way code like this behaves: > > :def process(L=[]): > : # 'x' always needs processed... > : L += ['x'] > : print L > : > :process() # prints "['x']" > :process() # prints "['x', 'x']"! > > We've been able to figure out what's happening, but it seems > counter-intuitive. > > If Python were changed so that default-argument, rvalue objects were > recreated each time a function is invoked, I think that it would be > intuitive (and efficient) if the object were only created when > necessary. Here's (approximately) another code snippet I've seen > recently: > > :def determine_default(): > : print "Why is this code executing?" > : return 1 > : > :def fun(arg=determine_default()): > : pass > : > :fun("value") > > Thanks, > Sam > _______________________________________________ > Python-3000 mailing list > Python-3000@python.org > http://mail.python.org/mailman/listinfo/python-3000 > Unsubscribe: > http://mail.python.org/mailman/options/python-3000/cvrebert%40gmail.com > _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
