Alex Martelli wrote: > This is the first time on this thread in which I'm glimpsing that you > mean 'when' not as in SQL (where it has just the same meaning as the > 'if' in Python's genexps/listcomps), but rather with the meaning that > any Pythonista would instinctively spell 'while'. Since AFAIK 'when' is > only used in SQL (out of widespread languages), using it with a > drastically different meaning would be an utter disaster, IMHO. The original post was in the context about dropwhile/takewhile. I may choose the wrong word "when". BTW, what does "when" do it SQL ? I only know about "where" which I believe is the closest equvialent of "if" in python generator comprehension/list expression.
To me when/while has a "sequence" element there whereas "where/if" don't. I didn't choose "while" because I know it is a key word already in python so I never thought about it being in this kind of construct, but thinking about it, "if" can be used in list expression then may be while can be used to. > > Right now, listcomps and genexps can be explained very simply as > equivalent to just the same nesting of for and if statement as they have > clauses in sequence. Adding a 'while' clause (or 'until', etc) would > unfortunately break this simple rule, and therefore make the whole > construct harder, not easier, to understand. Unless there are very > compelling and frequent use cases for such an addition, I doubt it's > worth even trying to make a patch in order to time it against > itertools.takewhile... I have no idea what it is involved or what about rules. I just raised a simple question because the whole dropping filter/map/reduce discussion I read gave me the impression that python is siding over in-line list/generator expression rather than the more traditional map/reduce/takewhile function call style. -- http://mail.python.org/mailman/listinfo/python-list
