Thank you for your answers!
Actually I did something similar to what niederle suggested: I called my python script within KNIME using a bash node, and then used a SDF reader to reimplant the data within the workflow.
I am pretty sure this is not the most straightforward way to do it, but it worked immediately for me.
If anyone has a better idea in the meantime new python snippets are released, don't hesitate to share it with me! ;)
Jose Manuel