In article <[EMAIL PROTECTED]>, Antoon Pardon <[EMAIL PROTECTED]> wrote:
> Op 2005-01-17, Steve Holden schreef <[EMAIL PROTECTED]>: > > There you go with the minutiae again. How about: > > > > "Don't use mutables as hash keys"? > > That sounds too dogmatic to my ears. I also find it > too selective. The problem with mutables as dictionary > keys is not specific to dictionaries. Everywhere you > have mutables in a container, it is possible that > mutating the object in the container will cause > problem. The main difference is: if you mutate a dict key you *always* have a problem. So don't do that. Mutating (say) a list item *only* is a problem if you (say) need that list to remain sorted. Lists don't magically remain sorted, so people generally sort it before they do some operation that expects a sorted list. > Heck even using mutables as arguments can > cause trouble. Why else the specific advice against > > def foo(p = []) > > type of arguments. So should we adopt the principles: > > Don't use mutables in containers Nonsense. > Don't use mutables as default values for parameters That's good advice in general. > Don't use mutables as arguments. Nonsense. > Don't assign one mutable to an other. Nonsense. Some newbies get surprised by Python's assignment-doesn't-copy semantics, but it's such basic knowledge (as well as a useful feature) that I simply don't understand you saying this. > I don't see a big difference between these principles > and the hash key principle, Than you haven't looked hard enough. > so in the end may be we > should just stick with the more general principle: > > Don't use mutables! > > > and be done with it. Ok, so you're indeed a troll. Just -- http://mail.python.org/mailman/listinfo/python-list
