Bizarre method keyword-arg bug.

Jasper jasper at peak.org
Mon Aug 18 10:32:12 CEST 2008


I'm stumped.  I'm calling a method that has keyword args, but not
setting them, and yet one of them starts off with data?!

The class definition begins like so:

class BattleIntentionAction( BattleAction ):
    def __init__( self, factionName, location, tactic='hold',
targetFacName='', terrainArgs=[], garrisonIds=[] ):
        self.terrainArgs = terrainArgs
        print terrainArgs

The constructor is called somewhere else, like so:
act = BattleIntentionAction( facName, self.location )


During this object's construction, terrainArgs is set to a list with
values corresponding to a previously created BattleIntentionAction!
Even more bizarre, the terrainArgs param is a testing formality, and
doesn't actually get used anywhere in my code -- the corresponding
attribute is always modified after object creation.  Furthermore, this
doesn't happen with the other keyword args...

Obviously, I'm glossing over a ton of code here, but I'm having a
tough time isolating this problem, as it seems to be very dependent on
events leading up to it.  It feels like the sort of memory stomping
bug I remember seeing from days of yore when I hacked C++. :-(


I frankly don't understand how "terrainArgs" can have a value if
nothing is passed for it on the calling invocation, short of some
obscure compiler bug (this is Python 2.4.3).  Am I being naive?  Is
there some way I could be bringing this about myself?

I can easily work around this weirdness by having the caller set
terrainArgs explicitly, but I can't shake the sensation that this
"fix" just masks some deeper flaw in my code.


Arg!
-Jasper



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