On using pickle with ROOT histograms

[Angel Campoverde]

Dear HSF people, 

I have found myself using pickle to serialize objects. Once in a while we use data that needs to be stored in histograms and becomes a class attribute. When pickling the object and trying to unpickle it with a version of python different from which was used to pickle, errors happen (e.g. 3.8 vs 3.10).

This means that we will either forever be stuck with a given version of python or we need to redo all the objects we pickled. 

Has anyone encountered this problem? I have talked to people and they have suggested that I use ROOT files to store my histograms, but my histograms are just an attribute of the object I am serializing, maybe 5% of that object. I would have to make the whole class a C++ ROOT object to be able to save it in a ROOT file, which seems much more involved. 

Another alternative would be a tool that stores the histogram's data and can, on demand return histograms. That data container, let's say a "hist_data" class, would be the attribute, not the histogram. I would be glad to know if anyone else has found this issue and how they have got around it.

Cheers.

[Graeme A Stewart]

Hi Angel

 

Traffic on this list is a bit weak these days. I would suggest that you ask the question in the PyHEP group, as it’s very much under their purview.

 

If you have a look here:

 

https://hepsoftwarefoundation.org/workinggroups/pyhep.html

 

You will find a link to their Gitter channel, where such things can be discussed with some of the gurus. (There is even a dedicated channel for histogram topics.)

 

Cheers

 

Graeme

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[Angel Campoverde]

Dear Graeme,

Thanks for the advice, now it is in the PyHEP-histogramming group.

Cheers.

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