On Thu, Jul 2, 2009 at 2:36 PM, Carl Banks<pavlovevide...@gmail.com> wrote: > On Jul 2, 3:12 am, Ulrich Eckhardt <eckha...@satorlaser.com> wrote: >> Bearophile wrote: >> > Ulrich Eckhardt: >> >> a way to automatically release the resource, something >> >> which I would do in the destructor in C++. >> >> > Is this helpful? >> >http://effbot.org/pyref/with.htm >> >> Yes, it aims in the same direction. However, I'm not sure this applies to my >> case. The point is that the resource handle is not just used locally in a >> restricted scope but it is allocated and stored. The 'with' is something >> that makes sense in the context of mutex locking, where you have a >> well-defined critical section. What I need is something similar to open(), >> which returs a file. When the last reference to that object goes out of >> scope, the underlying file object is closed. > > On CPython you can do it with a __del__ attribute. > > Warning: objects with a __del__ attribute prevent reference cycle > detection, which can potentially lead to memory (and resource) leaks. > So you must be careful to avoid creating reference loops with that > object.
WARNING-er: As Carl points out, adding a __del__ method actually makes it /less/ likely that your object will be cleaned up. __del__ is only useful if you have a complicated tear-down procedure. Since you come from C++ RAII land (my old haunt) your objects probably only allocate one resource each, or worse: a bunch of objects that allocate one resource each. In that case __del__ will always hurt you. The C++ temptation is to match every __init__ with a __del__. A better rule of thumb is to only add a __del__ method after confirming with someone else that it would be useful. Better still is to ask them by postal courier. For best results that someone should be your grandmother. > Note that file objects have a close method; you can explicitly close > it at any time. Your object should follow that example, and define a > close (or release, or whatever) method. I'd recommend making an > effort to call it and to rely on __del__ as little as possible. This. If you care enough about a resource to write a __del__ method you care enough to clean it up explicitly. 'with' blocks are very nice for that. -jack -- http://mail.python.org/mailman/listinfo/python-list
