pickle.dump protocol level

[Richard]

Hello,

I was creating a pet app and decide to give a try to python3...

After a couples wrong start with missing libs installation in one or the other of python2/3 I finally get it to work... But when I try to graph my db schema with pygraphviz I start to have this issue :

<type 'exceptions.ValueError'> unsupported pickle protocol: 3

I googled it and find this :

http://stackoverflow.com/questions/25843698/valueerror-unsupported-pickle-protocol-3-python2-pickle-can-not-load-the-file

I search the code base and pickle.dump is call like this :

pickle.dumps(self, pickle.HIGHEST_PROTOCOL)

So, I guess the problem kick in when I pass from python2 to python3 and get back in python2...

Could we lower the protocol level to prevent this issue simply??

I guess it would help web2py users transitionning their apps from python2 to python3 if they can start web2py py2 or py3 without having pickled object kind of unreadable...

Thanks

Richard

[Richard]

Should be related to : https://github.com/web2py/web2py/issues/834

I am not sure anymore what could have trigger this issue...

Will try to move my code into an other new clean generic app to see if goes away...

I may had launch python2 and python3 instance at the same time, I recall didn't close python3 instance properly (hit ctrl+z instead of ctrl+c)...

Richard

[Richard]

Moving code into an new generic shell app and restart with python2 let me workaround the issue...

But as soon as I restart with python3 it comes back... Admin app don't even work, I have to clear session ans error files to fix it...

Richard

[Niphlod]

either you run python 3 or you run python 2.

There's a reason why they span at least a major release :P

[Richard Vézina]

You mean once someone decide to move on py3 there is no way back? It could help a bit to refactor to be able to restart in py2 as long as the code base is still py2 compliant, for sure at some point you can't go back of course.

Richard

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[Paolo Valleri]

Any file created with pickle.dumps (for example session files) is not portable from python3 to python2.

I'd suggest adding an entry in the README (and/or in the book) to warn users when trying py3 (and going back to py2)

 Paolo

[Richard Vézina]

Hello Paolo,

Is there a way to allow it, I mean go back and forth as long as app code base allow it?

And if so, what would be the drawback of having such "feature"...

But I think, I understand the issue better : http://stackoverflow.com/questions/28218466/unpickling-a-python-2-object-with-python-3

It related to unicode and byte, mean encoding, so it would be a pita...

Yeah a good explanation in the README and the book would make things clearer and avoid having thread about that poping around all the time a new user fall on the issue.

Regards

Richard

[Richard Vézina]

Hey guys... We don't have release note about that....

https://github.com/web2py/web2py/releases

Richard