Q: Python 2.0 preliminary features?

[Jeremy Hylton]

>>>>> "GE" == Greg Ewing <greg.ewing at compaq.com> writes:

  GE> Also, to clarify Tim's rather waffly characterisation of when my
  GE> closures do or don't cause cycles, it's quite simple: they never
  GE> cause cycles unless you write code which makes them do so. This
  GE> is no worse than the situation with regard to cycles everywhere
  GE> else in the language.

I think this description is at least as waffly as Tim's :-).  It seems
to me that most of the interesting uses of lexical scoping necessarily
create cycles.  Is there a large class of uses that will not create
cycles? 

One of the prototypical uses of lexical scoping is functions like
these: 

def make_adder(num):
    def adder(x):
            global num
            return x + num
    return adder

In this case, adder maintains a reference to make_adder's
environment, and that environment maintains a reference to adder,
because adder was defined there.  So we have a cycle...

It seems odd to propose adding lexical scoping to Python, and then
tell people not to write code like make_adder.

Jeremy