# Problem with RDataFrame::Snapshot in python

Continuing the discussion from Problem with RDataFrame::Fill in python:

I think the same problem affects the Snapshot function when calling it in python. But in this case there is no easy workaround.

simone

ROOT Version: 6.20/04
Platform: linuxx8664gcc
Compiler: 9.3.0

@eguiraud, @etejedor Any comment?

Hi Simone,
can you provide a few lines of python that reproduce the issue? Snapshot can certainly be invoked from python, see e.g. https://root.cern.ch/doc/master/df007__snapshot_8py.html

Cheers,
Enrico

Hi Enrico,

sorry I was too quick in posting the problem. I missed from other examples I looked at that one should define the ColumnNames as a c++ vector. I was calling Snapshot like this:

``````rdf.Snapshot('tree', 'file.root', ['my_var'])
``````

As it was suggested in the jira ticket opened follwing the mentioned forum post, and using such a list does not work. Using a previously defined ROOT.vector(‘string’) fixes the issue.

Thank you,

simone

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