Python3, __slots__ and serialization

Ned Batchelder ned at
Sat Feb 8 19:29:34 CET 2014

On 2/8/14 1:06 PM, Eric Jacoboni wrote:
> Hi,
> Say i want create a class with a __slots__ tuple in order to prevent
> creation of new attributes from outside the class.
> Say i want to serialize instances of this class... With pickle, all is
> ok : i can dump an object to a file, then reload it.
> With PyYAML, i can dump an object to a file, but trying to reload it fails.
> If i comment out the __slots__ tuple, all is fine but, then, the class
> is "open"... Is there some magic to have both a __slots__ tuple and a
> working yaml.load() ?

Preventing attribute creation runs counter to Python's philosophy, so it 
doesn't surprise me that it causes problems.  There might be a way to 
make it all work together, but I don't know.

__slots__ wasn't meant to be a way to prevent attribute creation, it was 
meant as a way to save space by avoiding the need for an attributes 

Why do you need to prevent attribute creation?  If someone uses your 
class and wants to use it in ways you didn't anticipate, why should you 
try to stop them?

Ned Batchelder,

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