Hello,
I am having trouble with throwing class instances around. Perhaps I'm
approaching my goals with the wrong solution, but here's nevertheless a
stripped down example which demonstrates my scenario:
#------------------------------------------------------------------------------------------
class foo:
tests = {}
def __init__( self, id ):
try:
me = self.__class__.tests[ id ]
except KeyError:
print "Did not exist, initializing myself.."
self.attr = "exists"
self.__class__.tests[ id ] = self
else:
print "Already exists! Re-using existing instance"
self = me
print "Me", self.attr + "!" # line 18
def yo(self):
return self.attr # line 21
def main():
a = foo( "test" )
print "ATTR:", a.yo()
b = foo( "test" )
print "ATTR:", b.yo()
if __name__ == "__main__":
main()
#------------------------------------------------------------------------------------------
This is the output:
Did not exist, initializing myself..
Me exists!
ATTR: exists
Already exists! Re-using existing instance
Me exists!
ATTR:
Traceback (most recent call last):
File "cpClass.py", line 32, in ?
main()
File "cpClass.py", line 29, in main
print "ATTR:", b.yo()
File "cpClass.py", line 21, in yo
return self.attr # line 21
AttributeError: foo instance has no attribute 'attr'
#------------------------------------------------------------------------------------------
What the code attempts to do is implementing a, to the API user, transparent
memory-saver by ensuring that no more than one instance of the class foo
exists for a particular id. E.g, the user can simply "create" an instance and
if one not already exists, it is created.
First of all; am I approaching the goal with the right solution?
The way I do fails, obviously. The line 'self = me'(scary..) doesn't really
work for the attribute attr; the attribute exists on line 21, but it fails
when yo() tries to access it. What have failed? Is it a namespace scope
issue? Do 'self = me' do what I think it should?
Cheers,
Frans
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