Thomas Wouters wrote: > On 1/18/07, *Larry Hastings* <[EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>> wrote: > > > > I just ran a quickie experiment and determined: when leaving a > scope, variables are deleted FIFO, aka in the same order they were > created. This surprised me; I'd expected them to be deleted LIFO, > aka last first. Why is it thus? Is this behavior an important > feature or an irrelevant side-effect? > > > Please regard it as an irrelevant side-effect. If you want objects to > be cleaned up in a particular order, you should enforce it by having > one of them refer to the other. A great many details can affect the > order in which variables are cleaned up, and that only decreases > refcounts of the actual objects -- a great many other details can then > affect the order in which any objects left with a 0 refcount are > actually cleaned up. Even not counting the more complicated stuff like > GC and funky __del__ methods, just having 'import *' or a bare 'exec' > in your function can change the order of DECREFs.
I imagine this would be important to someone expecting system resources to be cleaned up, closed, deallocated, or returned inside of __del__ methods. Someone coming from C++ might expect LIFO behavior because common idioms like RAII (Resource Allocation Is Instantiation) don't work otherwise. A Java programmer wouldn't care, being used to cleaning up resources manually with a try...catch...finally. I'm just putting a possible motivation on the concern. It happens that the Pythonic Way is also the Java Way in this area: don't expect any specific deletion order (don't even expect a guaranteed call to __del__), and manually clean up after yourself. As a warning, this has been the subject of a great many flame wars between C++ and Java programmers... Neil _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
