[Python-Dev] 2.5 and beyond (original) (raw)

jan-python at maka.demon.nl jan-python at maka.demon.nl
Sun Jul 2 13:58:55 CEST 2006

Hi everyone, Even though I'm new on this list I think I've got something sensible to say on this one. (I've been following this list a bit through the archives)

Andrew Koenig wrote:

You seem to be right -- the problem is not that Python is lexically scoped, but that when you define a variable with =, it leaks out into the surrounding function scope.

So maybe what I meant when I asked for lexical scopes was two things:

1) Every indentation level should be a scope; 2) In general, variable definitions should not leak into surrounding scopes. I realize that (2) is too simplistic. Someone who writes

I believe the problem has nothing to do with how many scopes a block/function definition has, but with what the lambda does with the scope it's given. Currently it remembers the block and looks up the nescessary variables in it when it's invoked. I think it shoud should have just taken the values of the needed variables and rememberd those as it's own local variables. So the closed over variables become just local variables initialised to the value they have in the outer scope.

Without having any blocks to be confused about, I think this is counterintuitive as well:

x = 1 f = lambda: x x = 2 g = lambda: x f() 2 g() 2

I think it should have been: ....

f() 1 g() 2

Using the lambda x=x: x trick gives exactly this behaviour because it apparently does copy the value of x. As far as I can see it also solves the

for i in range(10): ... a.append(lambda: i) case, and other similar examples. (However, this would probably be a to big change for 2.5)

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