[EMAIL PROTECTED] > My questions are: > 1) under normal conditions (no exceptions) is there a guarantee, that > __del__ of > all instruments is called at the end of measurement()? > > 2) if an exception is thrown, will all instruments be deleted if the > error > occurs in run() ? > (only the instruments already initialized if the error occurs > in setup() )? > > I am using CPython (on WinXP) and there are no reference cycles between > the instruments. > > I have to stress again that a reliable finalization is important and > cannot wait > until the interpreter shuts down. > > I have tried this and it seems to work but this is of course no > guarantee.
On the plus side, Python does guarantee destruction in the absence of cycles when the last reference disappears. If there is a cycle, you have to wait for GC. If you can't wait, then schedule a gc.collect() to run periodically. On the minus side, this is a somewhat brittle and error-prone design strategy. A single, accidental persistent reference is sufficient to cause failure -- that is a land-mine for all future maintainers of your code. It is better to make explicit tear-down calls and to wrap finalization is a try/finally suite. The simplified code in your post suggests that the instrument shut-off can be placed at the end of the run() method -- loosely translated as turn-off the lights when you're done. An alternative strategy is to periodically poll resources and shut them off if they are not in use -- loosely translated as having a security guard turn-off any coffee-pots that were left on by frazzled programmers as they leave at odd hours of the night. Raymond -- http://mail.python.org/mailman/listinfo/python-list
