On Aug 24, 12:05 am, Mel <mwil...@the-wire.com> wrote: > seb wrote: > > On Aug 23, 6:18 pm, John Posner <jjpos...@optimum.net> wrote: > [ ... ] > >> How about using a generator expression instead of a list? > > >> for i in (x for x in range(10) if x > 5): > >> print i > > >> -John > > > Indeed, but we could have the same syntax than for generators but > > directly in the for statement as in > > for variable in generator if condition: > > body > > > Is there a special reason for not doing so ? A rejected PEP ? > > Well, the Zen of Python does say > > There should be one-- and preferably only one --obvious way to do it. > > Beyond that, I refer you to Gerald M. Weinberg's _The Psychology of Computer > Programming_, specifically chapters 11 and 12, about Programming Languages, > and their design. > > The proposal creates an case where one particular pair of syntactic > constructs can be mooshed together. OK for them, but everything else > becomes an exception; what about > > while a==c if b != d: > > why not > > if b != d while a==c: >
what would be the unambiguous meaning of any of these forms ? they could be interesting but I do not understand them (yet!). > or > > for a in range(7) if os.name == 'posix': > > It winds up burdening the programmers with remembering which constructs are > and which are not mooshable. Weinberg gave an example: FORTRAN had some > stringent rules for what expressions were and were not allowed as array > subscripts. The result was that many programmers couldn't remember all the > rules, and often avoided using legal forms, having forgotten they were > legal. indeed, the language features should stay as orthogonal as possible (at least as a general rule) > > Maybe the line was already crossed when list comprehensions came into being, > still, the damage is localized in a particular context: building a list. It > isn't out creating wild options in the program control flow at large. > indeed and it proved to be very useful & successful. one cannot recommend to mix all features together as a general rule but using common sense and practice, we can have some exceptions that are definitely worth. > Mel.- Hide quoted text - > > - Show quoted text - -- http://mail.python.org/mailman/listinfo/python-list
