[Python-Dev] Deletion order when leaving a scope? (original) (raw)

Thomas Wouters thomas at python.org
Thu Jan 18 10:55:33 CET 2007

On 1/18/07, Larry Hastings <larry at hastings.org> 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.

-- Thomas Wouters <thomas at python.org>

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