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detecting property modification


I think it is easier to explain my question with a short example:

class Body:
def __init__(self, pos):
self.__dict__['pos'] = pos

def __setattr__(self, name, value):
if name == 'pos':
print 'pos changed to', value

self.__dict__[name] = value
>>b = Body([0, 0])
b.pos = [3, 4]
pos changed to [3, 4]
b.pos[0] = 5 # How do I detect this in the Body?

I would like to print 'pos changed to [5, 4]' when pos is modified
with direct access to the pos object (i.e. b.pos[0] = 5)
My first instinct is to modify the Body's __dict__ by using
I don't have any experience with meta classes but from what I remember
this should be possible but I thought there could be a simpler way to
do this.

What is the Pythonic way to do this? Can anybody provide a short
example for either case (with or without metaclasses).

Dec 21 '07 #1
0 733

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