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recursion error using setattr and getattr

P: n/a
Hi,

I m trying to implement an object which contains lazy" variables. My
idea is to alter the getattr and the setattr methods. However I keep
on getting a recursion error.

My idea is that the lazy variable can be stored in a variety of
places, Database, PyTables etc. The lazy variable is a large variable
and so I dont want to hold it in memory all of the time, I d rather
just get it when needed and then store it for future work. Most of the
work will be done using var1 and var2

So ......

class LazyBase(object):
self.var1 = 0
self.var2 = None
def __init__(self, name):
self.name = name
def __str__(self):
return self.name
def __setattr__(self, attr, k):
if attr == "var1":
if self.var1 != k
self.var1 = k
if self.lazy != None
self.lazy = None
elif attr == "var2" :
if self.var2 != k
self.var2 = k
if self.lazy != None
self.lazy = None
else:
raise Exception("Attribute")
class SQLLazy(LazyBase):
def __init__(self, name, table="test_table"):
self.table = table
LazyBase.__init__(name)
self.lazy = None
def __getattr__(self, attr):
if attr == "lazy":
if self.lazy == None: # problem line I think
print "Hit Database"
# use sqlalchemy to get the variable
# set self.lazy = lazy
return self.lazy
else:
return self.lazy
else:
try:
return Lazy.__getattr__(attr)
except:
raise Exception("Attribute Exception")
def __setattr__(self, attr, k):
if attr == "lazy"
raise Exception("Cannot alter lazy")
else:
try:
Lazy.__setattr__(attr, k)
except:
raise Exception("Attribute Exception")

if __name__=='__main__':
spam = SQLLazy("Test")
spam.var2 = 10
print spam.lazy
print spam.lazy
spam.var2 = 5
print spam.lazy

I m expecting the output:
Hit Database
Lazy Variable
Lazy Variable
Hit Database
Lazy Variable

However I just get recursion errors. Does anyone have any ideas how I
can implement this sort of thing through my current method, or is
there a better way to accomplish this.

THanks

Nathan
Jun 7 '07 #1
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