how to count lines in a file ?

[Alex Martelli]

Donn Cave wrote:
        ...
> the garbage collection changes to the C Python that we use have not
> compromised its reference count driven behavior at all.

Not yet.  If one day a smart non-RC collector shows the potential
for, e.g., 20% or 25% speedup, though, what then?


> You're just looking at the other Python there, Jython.  Its object
> lifetime policy is Java's, and that doesn't support timely finalization.
> There's your spanner.

"Timely finalization" plays very badly with efficient garbage
collection.  You can count on a good GC system to NOT guarantee
"timely finalization", more or less.

One thought I've toyed with, at times, is to have the optional
ability to mark a few objects as _requiring_ stricter finalization
semantics than the run-of-the-mill kinds of objects.  E.g., files
could be marked that way.  References to such special objects would
then also have to be special and require the typical RC overhead
when manipulated.  Cycles involving such objects would still be
a bother, of course.  Alternatively, all references to such objects
could be special kinds of weak references EXCEPT one reference
held in the creation frame -- the object would then, differently
from all others, be owned by one specific primary reference and
finalized (with all other references to it, being weak, becoming
invalid) when that one specific primary reference goes away.

Semantics could be per-object rather than per-type, e.g.:

        local(open('foo','w')).write('hi!\n')

would not INSTANTLY close foo, but it WOULD close it as part
of the cleanup for the current frame thanks to the hypothetical
local() builtin.  The .write() call would in this case be
happening on a kind of weak proxy for the file object.

When I get to this point in my musings I typically tend to
get lost wondering how to UN-localize such an object so that
after the fact it's possible to get a more persistent reference
to it, etc, etc.  But maybe even the simplest kind of 'local()'
could already have some usefulness, perhaps enough to make it
worth experimenting with.


Alex