In article <XnsA0927750022F4duncanbooth@127.0.0.1>, Duncan Booth <duncan.bo...@suttoncourtenay.org.uk> wrote: >Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: > >> On Fri, 13 Jul 2012 12:30:47 +0000, Albert van der Horst wrote: >>> The worst of is, of course, = for assignment instead of := . This is >>> a convention that Python follows, to my dismay. >> >> *shrug* >> >> The worst is to use = for both equality and assignment, like some >> BASICs. At least Python does not allow assignment as an expression, so >> you can't make the typical C error of: >> >> if x = y: do_something() # oops meant x == y >> >Technically of course Python doesn't have assignment, it just binds names. > >Albert raised the subject of Algol 68 which if I remember correctly used := >for assignment and = to bind names (although unlike Python you couldn't >then re-bind the name to another object in the same scope).
Algol 68 is very particular about this indeed. For instance they have a whole theory behind real x; x := 17.; This is considered an abbreviation of ref real x = loc real; x:= 17; So x is a reference bound to a freshly generated local real. You see = and that means you can't ever break that relationship. On the left side of a := it is required to have a ref something. Because that generates a pretty clear context, you have considerable leeway on the right side, that is cast into the something. real x= 18.; x := 15.; is right out. If you want to rebind something you need a ref which is really a ref ref. Then you can only switch bindings between different types. So it is totally different from Python. I never thought about = in python to mean binding to set it apart from the Pascal := , instead of being a c-ism. Still my mathematical mind is bothered about the sequence ( legal in FORTRAN , C Python ) X = 1 <separator> X = 2 Groetjes Albert >-- >Duncan Booth http://kupuguy.blogspot.com Groetjes Albert -- -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- being exponential -- ultimately falters. albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst -- http://mail.python.org/mailman/listinfo/python-list
