[Python-ideas] For-loop variable scope: simultaneous possession and ingestion of cake

[Ron Adam]

Carl Johnson wrote:
> Why does the evil default args hack work? Because it immediately 
> evaluates the argument and stores the result into the lambda object's 
> default values list. So, what we need is a keyword that means 
> "immediately evaluate the argument and store the result, instead of 
> looking up the name again later." Since I can't think of a good name for 
> this, I will use a terrible name for it, "immanentize."


Yep, that is terrible!  ;-)


I'm really starting to see this as a non-problem after reading all these 
posts.  This particular problem is solved much nicer with a class than a 
function.

I have two reasons for this, one is classes are the natural structure to 
use if you want to save a state.  And the other is I would actually prefer 
that functions never save states, or even closures.  (but that would break 
a lot of decorators.)

Here is an example that works as expected with no magic or hidden behaviors.


class Caller(object):
    def __init__(self, f, *args, **kwds):
        self.f = f
        self.args = args
        self.kwds = kwds
    def __call__(self):
        return self.f(*self.args, **self.kwds)

def id(i):return i

L = []

for n in range(10):
    L.append(Caller(id, n))

for f in L:
    f()


You could go one step further and make the class more specific to the 
situation it is being used by defining the __call__ method to do what you 
want instead of using a stored function reference.



Something I think would be more beneficial to solve is to be able to pack 
and unpack entire function arguments into one signature object easily and 
automatically.

def foo(***aks):
   ...


Ron