Functions as Objects, and persisting values

[Rich Harkins]

[snip]
> The "thing" you observe here is a called a closure. It consists of the 
> local variables surrounding e. So as long as you keep a reference to e, 
> you keep one to the variables of d itself.
> 
> Diez

More specifically though it keeps references to the requested variables
only:


def closed():
    x = global_x
    y = "Y_VAR"
    def inner():
        return y
    return inner

class Destroyable(object):
    def __del__(self):
        print "DESTROYED"

global_x = Destroyable()
inner = closed()
print inner()
del global_x
print inner()
print "HERE"

You will get:

Y_VAR
DESTROYED
Y_VAR
HERE

If the entire dict of closed() was kept you would have seen:

Y_VAR
Y_VAR
HERE
DESTROYED

Since closed hadn't been destroyed yet: thus there was only one
reference remaining to global_x after closed() and inner() were called.

Rich