Since you asked: The None value comes from a Python program marking values where no input data was supplied. Feasible, but some information is lost, because None simply states that there is no value available whereas NaN says that something went wrong during the calculations.
It would require replacing None values with ' NaN' in the output routine. Your workaround of using NaN instead of None works. If there are headers in the file, you have to use the CSV tab which does not handle None at all. It is possible to load data files containing None in the Standard tab but it shows some errors. When I do so, it seems to ignore the descriptors. 2) I have tried combining the data into a single file & then reading those data in as blocks. 1) I have tried importing a second data file, but it seems to displace the first I cannot see both of them at the same time. It features GUI, command-line, and scripting interfaces. to import multiple data files into Veusz. It can create line graphs, XY plots, histograms, shapes, images, ternary plots, polar plots, box plots, vector field plots and contour plots.
It looks to me, that Veusz cannot handle None values like Python does, which is a bit surprising to me, because it is written in Python. Veusz is a scientific plotting package, designed to create publication-ready Postscript, PDF or SVG output. The column is marked as text if None is in the first row.The column is split into two if None is in the middle of the column.It does not work with None in the first data row.The CSV import works well with NaN in the first data row.