spir, 30.11.2009 11:24: > Below startup definitions: > > x = 1 > > def f(): > n = 1 > def g0(a): > print (x + n + a) > return g0 > > I'm surprised the snippet below works as expected (py 2.6) without any trick: > > g = f() > g(1) # --> 3 > > This means a (real) closure is built for g0, or what?
Yes. > Thought I would need instead to use the old trick of pseudo > default-parameters: > > def f(): > n = 1 > def g0(a, n=n, x=x): > print (x + n + a) > return g0 > > to let the inner func g0 "remember" outer values. Why is this idiom used, > then? Has something changed, or do I miss a relevant point? Different use case. The above uses default arguments for n and x that can be overridden by callers, but that have a value if callers do not pass them. Values in closures can only be modified by the owner(s) of the names that participate in the closure (i.e. the function f in this case). > The bit below also works: > > x = 2 > ... > g(1) # --> 4 x is not in the closure, it's a global name. > the func's behaviour and result depend on arbitrary external values > (referentially opaque). What do you think? It's a matter of how you use it. Closures make a lot of sense for many cases, but there are certainly also cases where using them feels like a goto - just like global variables. Stefan _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
