On Sat, 04 Oct 2008 18:36:28 +0200, Bruno Desthuilliers wrote: >> Yes I know that sets have a remove method (like lists), but since >> dictionaries don't have a remove method, shouldn't sets behave like >> more like dictionaries and less like lists? IMHO del for sets is quite >> intuitive. > > For lists, del a[x] means 'remove item at index x'. For dicts, del a[x] > means 'remove key:value pair which key is x'. In both cases, del a[x] is > meaningful because a[x] is meaningful. Sets are neither ordered nor > indexed, and can't be subscripted. So "del aset[x]" is IMHO as > meaningless as 'aset[x]' is. Using this syntax for an operation which > semantic is the same as alist.remove(x) would be at best inconsistent > and confusing.
Consider the mutable built-in collections set, dict and list, and how they remove elements: aset.remove(x) alist.remove(x) del adict[x] Would it really be "confusing" if sets used the same interface as dicts use? I don't think so. What else could "del aset[x]" mean other than "delete element x"? Lists are the odd one out, because del alist[x] is used to remove the element at position x, rather than removing an element x. But because sets are unordered, there's no ambiguity between element x and the element at position x. In that regard, sets are just like dicts, and it is a perfectly reasonable position to take that hypothetically sets could use "del aset[x]" instead of "aset.remove(x)". But on the other hand, if you can write "del aset[x]", why can't you write "y = aset[x]" or "aset[x] = z"? Neither of these seem useful or sensible, although at a stretch we could make "y = aset[x]" equivalent to "y = x in aset". Although there's no technical reason why sets can't have a __delitem__ method but no __getitem__ and __setitem__ methods, for consistency it does seem rather unusual. All this may seem academic, but consider the Bag (Multiset) data type. With a Bag, you need to have two commands: "remove element x entirely", and "remove one copy of element x only". To my mind, the natural API for that is: del abag[x] # remove element x entirely abag.remove(x) # remove one copy of element x only -- Steven -- http://mail.python.org/mailman/listinfo/python-list
