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/ -- Steven -- http://mail.python.org/mailman/listinfo/python-list
