Mike Meyer wrote: > "Shai" <[EMAIL PROTECTED]> writes: > > > They're called "Special vars", and you need to define them (unlike > > local LISP variables, which behave essentially like Python vars), but > > then you use them just like other vars (that is, you usually bind them > > with LET). This is the first I hear about them being ill-considered in > > LISP; http://www.gigamonkeys.com/book/ is a recently published LISP > > book which recommends them. I don't know about Scheme, but I think it > > does have them. > > I'm pretty sure scheme doesn't have dynamically bound variables. I > just went through r5rs to check, and couldn't find them. >
Yes, you're right. One learns. > > dynamic x=10 > > def bar(): > > print x > > > > This looks different from what I understood before. You're now > declaring the variable dynamic in the global scope, rather than in the > function that makes it dynamic. This is a *much* more palatable > situation. > This is indeed different from what I said first. It copies the Common LISP construct without regard to consistency with the Python global construct. > Globals are lexically scoped. As such, you can find the defintion of > the variable by examining the module that includes the function. Yes, > other modules can reach into your module and change them - but you can > find those, because they reference your module by name. > > A dynamic variable declared so in a function has no such clue > associated with it. If the variable is declared dynamic in the module > of the enclosed function, that provides a contextual clue. In my original proposal, dynamic variables are seen as globals from the function in their module which reads them; no more, no less. The important point I want from dynamic scope is the time-locality of asignments, that is, the fact that they are undone when the (lexical) scope of the new binding ends. This allows the use of globals, with a lot less fear of unintended interactions between users of the module (well, this is only accurate until multithreading enters the picture, but that can be handled too). [rest snipped] -- http://mail.python.org/mailman/listinfo/python-list
