On Thursday 16 December 2010, 00:56:31 Steven D'Aprano wrote: > On Wed, 15 Dec 2010 21:10:05 +0100, Hans-Peter Jansen wrote: > > Since this is a major pitfall, it might be worth mentioning, that > > mutable default arguments are generally a bad idea, as the default > > arguments are evaluated just once, hence e.g. using an empty list > > might contain the items, that were appended in earlier calls of > > this method.. > > It's only a pitfall for users who expect that default arguments are > re- created every time you call the function; it's only a bad idea > for code which relies on the default arguments being re-created each > time. > > If you hold misunderstandings about the behaviour of a language, > you'll have trouble understanding what code does. Default arguments > are no different from any other feature. > > > Code, that _relies_ on such behavior should be yanked instantaneous > > and the producer of such code should be punished with coding APL¹ > > on a dubeolsik hangul keyboard² for a year at least.. > > Python code that relies on default arguments to *not* be re-created > on each function call is no worse than (say) Ruby code that relies on > default arguments *to* be re-created each time. > > I don't mean to be elitist (ah, who am I fooling, of course I do), > but when coders of the skill and experience of the Effbot and Guido > use mutable defaults, who are you to say they shouldn't? > > http://effbot.org/zone/default-values.htm > http://www.python.org/doc/essays/graphs/
Hmm, thanks for the pointers, Steven. I stand corrected, as I won't argue with taste.. I like the part about the disastrous results specially. If such code would be used in any collaborations, I would expect an explicit comment at least. Pete -- http://mail.python.org/mailman/listinfo/python-list
