I guess (hope!), we finally found the problem.
It seems like we do not support the full range of available numpy.dtypes, yet, but mostly the ones that exactly match the data types available in KNIME (e.g. numpy’s int32 matches KNIME’s Number (Integer), int64 matches Number (Long), etc.). Other, less common data types such as uint16 do not get recognized as “KNIME-native”. That’s why KNIME looks for serializer extensions that are able to handle the type but doesn’t find one. Somewhere on the way, the specific type (e.g. uint16) gets lost, that’s why the error message only states a rather broad “[…] python type “int””.
To temporarily work around this issue, please make sure to convert all affected columns - i.e. all integer columns that are not of dtype int32 or int64 - to one of the supported types. E.g., like this:
output_table.your_affected_column = output_table.your_affected_column.astype("int32").
This fixed the problem on my local machine. Please let me know if the problem persists after applying the workaround.
We will extend our data type support as fast as possible.
Again, sorry for the inconvenience.
Marcel