On Apr 2, 5:29 pm, Bjoern Schliessmann <usenet- [EMAIL PROTECTED]> wrote: > Laurent Pointal wrote: > > And so the solution to add "global foo" before using it. > > Didn't you read his final question? > > | All of a sudden, tiny() can see the global variable "foo". Very > | confusing! Why is it that tiny() sometimes can, and sometimes > | can't, see the global variable "foo"? > > I have no explanation for this, but I'm interested in one, too. > > Regards, > > Björn
Laurent Pointal did explain this. "foo" is considered to be a local variable (scope limited to the function) if it's being assigned to in a function and there's no "global foo" statement. So even the "foo" before the actual assignment will refer to the local variable. But the local variable hasn't been assigned yet at that point and an exception is thrown. Yes, one could have a perfectly working function, then add an innocent-looking assignment statement at the very end of the function, and suddenly you'd get an exception thrown at the beginning of the function where that variable is used - Far away from the place where the modification was made. Why does it work like this? Couldn't it be somehow more uniform or less surprising? Well, if one had to define "global foo" even when one were to just read the variable foo, that'd be a pain in the ass. You'd have to use "global math" to use math module in a function and "global anotherFunction" to call anotherFunction, and so on. There's plenty of stuff in the global scope that you don't normally assign to. Another option would be to scrap "global" keyword and let "foo = bar" do an assignment to the global variable if a global variable named "foo" exists, but create (or assign) to a function local variable if it doesn't exist. That'd work but programming would be horrible. Now you'd have to know all the symbols that exist at the global scope, because if you accidentally accessed a global variable instead of local, your function would probably have undesirable side-effects. Now, name clashes could be solved with a naming convention (which could be enforced at the language level). It could be possible that all accesses to global scope would have to be prefixed by some symbol like $. E.g. "$foo = 4; foo = 6" where former assigns to global foo, latter to local foo. That's one option that might work and be somewhat readable.. But not a good tradeoff IMO, considering how rarely global assignment is needed and how often global variables are read. A remaining option is to use different operator for assignment and initialization. So you'd have to do e.g. "a := 4; a = 7". I'm not sure Pythonistas would prefer this either, although many other languages choose this route (through lets or declarations typically). -- http://mail.python.org/mailman/listinfo/python-list
