John Williams <jrw@pobox.com> wrote in news:3E414335.7030704@pobox.com:
> Why not combine the "with" and "local" statement ideas? Change the
> "with" statement so that there is no __enter__ method, and call __del__
> where there current proposal calls __exit__.
If you put in your suggested check for getrefcount, then you can't port
this to systems with no refcount (such as Jython) and this use of __del__
conflicts with Jython's use.
Also, if you try to reuse __del__ in this way you are introducing another
possible place where it can go wrong (if someone has saved a reference to
the controlled variable and your assertion fails), whereas with __exit__
you don't have to insist that all other references have gone.
Indeed, if the variable is controlling a resource, such as a mutex, you
might very well want to maintain a list of all controlled resources. The
__exit__ can remove self from whatever data structures refer to it, but you
would have to do it manually before letting the __del__ be called.
Finally consider:
f = file(...)
try:
DoSomethingWith(f)
finally:
assert sys.getrefcount(f) == 2
del f
# f is guaranteed dead, so f.__del__ is called
If 'DoSomethingWith' throws an exception, the reference count for f is not
2 as 'f' is still referred to from the stack backtrace that someone may
wish to inspect.
--
Duncan Booth duncan@rcp.co.uk
int month(char *p){return(124864/((p[0]+p[1]-p[2]&0x1f)+1)%12)["\5\x8\3"
"\6\7\xb\1\x9\xa\2\0\4"];} // Who said my code was obscure?
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