@Bob_Nisbet the in and out syntax would look like this for pandas dataframes.
import knime.scripting.io as knio
import numpy as np
import pandas as pd
# data from KNIME to Python (pandas)
df = knio.input_tables[0].to_pandas()
# data from python (pandas) to KNIME
knio.output_tables[0] = knio.Table.from_pandas(df)
KNIME would work internally with Arrow format
https://docs.knime.com/latest/python_installation_guide/index.html#usage-examples