Митя wrote:
I have a class which I want to save it's data automatically on disc,
when it's destroyed. I have following code:
from cPickle import dump
class __Register(object):
def __init__(self):
self.dict = {}
def __del__(self):
fh = open('aaa', 'w')
dump(self.dict, fh)
fh.close()
g_register = __Register() # global instance. I do not destroy it
manually, so destructor is called on iterpreter exit
But when g_register is being destroyed, dump seems to be already dead,
so I get:
Exception exceptions.TypeError: "'NoneType' object is not callable" in
<bound method __Register.__del__ of <MyWiki.Register.__Register object
at 0x835a74c>> ignored
can I somehow save my data from destructor?
the order of __del__ execution is quite unreliable (depending on
implementation/version of Python).
Also there is problematic/circular garbage (gc.garbage).
=>
1. For algorithmic use cases see 'with' statement
http://python.about.com/od/gettingstarted/qt/py25WITH.htm
2. For data structure trees implement your own register/deregister
book-keeping. Often a kind of "second" container-refcount
attribute does it at core in cases with multiple but non-circular
linking.
Yet, to get the effect in a cheap way, one can often do something
like this:
Add those objects also to a global container
g_reg_containter.add( myObject )
Then periodically and at critical times (and maybe finally
sys.exitfunc) after gc.collect() check the sys.getrefcount(obj)
(or the "second" refcount) to fall below "1 plus number of extra
local refs". In case execute your obj.__deregister() or so ...
Robert
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