lambdas

[Craig Yoshioka]

Sorry, the first example should be:

class Status(object):
	def __init__(self,definitions):
		for key,function in definitions:
			setattr(self,key,property(function))

On Jun 14, 2010, at 3:06 PM, Craig Yoshioka wrote:

> I'm trying to write a class factory to create new classes dynamically at runtime from simple 'definition' files that happen to be written in python as well.  I'm using a class factory since I couldn't find a way to use properties with dynamically generated instances, for example:
> 
> I would prefer this, but it doesn't work:
> 
> class Status(object):
> 	pass
> 
> def makeStatus(object):
> 	def __init__(self,definitions):
> 		for key,function in definitions:
> 			setattr(self,key,property(function))
> 
> this works (and it's fine by me):
> 
> def makeStatus(definitions):
> 	class Status(object):
> 		pass
> 	for key,function in definitions:
> 		setattr(Status,key,property(function))
> 	return Status()
> 
> but I would also like the functions to only be evaluated when necessary since some may be costly, so I want to do the following:
> 
> def makeStatus(definitions):
> 	class Status(object):
> 		pass
> 	for key,function,data in definitions:
> 		setattr(Status,key,property(lambda x: function(data)))
> 	return Status()
> 
> but all my properties now act as if they were invoked with the same data even though each one should have been a new lambda function with it's own associated data.  It seems Python is 'optimizing'?  all the lambdas to the same object even though that's clearly not what I want to do.  Anyone have any suggestions as to:
> 
> 1) why
> 2) what I should do
> 3) a better way in which to implement this pattern
> 
> 
> Cheers!,
> -Craig
> -- 
> http://mail.python.org/mailman/listinfo/python-list

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