Donovan Baarda <[EMAIL PROTECTED]> wrote: > > On Fri, 2006-02-03 at 11:56 -0800, Josiah Carlson wrote: > > Along the lines of "not every x line function should be a builtin", "not > > every builtin should have syntax". I think that sets have particular > > uses, but I don't believe those uses are sufficiently varied enough to > > warrant the creation of a syntax. I suggest that people take a walk > > through their code. How often do you use other sequence and/or mapping > > types? How many lists, tuples and dicts are there? How many sets? Ok, > > now how many set literals? > > The absence of sets in early Python, the requirement to "import sets" > when they first appeared, and the lack of a set syntax now all mean that > people tend to avoid using sets and resort to lists, tuples, and "dicts > of None" instead, even though they really want a set. Anywhere you see > "if value in sequence:", they probably mean sequence is a set, and this > code would run much faster if it really was, and might even avoid > potential bugs because it would prevent duplicates...
Maybe they mean set, maybe they don't. 'if obj in seq' is used for various reasons. A quick check of the Python standard library shows that some of the uses of 'if obj in tuple_literal' could certainly be converted into sets, but that ignores the performance impact of using sets instead of short tuples (where short, if I remember correctly, is a length of 3, check the python-dev archives), as well as the module-level contant creation that occurs with tuples. There was probably a good reason why such a thing hasn't happened with lists and dicts (according to my Python 2.4 installation), and why it may not happen with sets. A nontrivial number of other 'if obj in seq' instances actually need dictionaries, the test is for some sort of data handler or headers with a particular name. - Josiah _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
