changes from altair1 to altair2?

I’m taking altair1 code and trying to make it work with altair2 (also a switch to python3). Not asking anyone to debug my code, but chart.savechart fails with a vega-lite schema validation error I’ve never seen before.

Is there any sort of porting guide that says “if you did this in altair1, it doesn’t work any more, do this instead”?

    chart.savechart(os.path.join(outputdir, name) + '.' + fileformat)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/altair/vegalite/v2/api.py", line 374, in savechart
    return self.save(fp, format=None, **kwargs)
...
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/altair/utils/schemapi.py", line 237, in to_dict
    raise SchemaValidationError(self, err)
altair.utils.schemapi.SchemaValidationError: Invalid specification

        altair.vegalite.v2.schema.channels.Column, validating 'additionalProperties'

        Additional properties are not allowed ('axis' was unexpected)

[domoritz]

Good timing. We just merged https://github.com/vega/vega-lite/pull/3943, which adds support for header. Once this is released and a new version of Altair is out, you can use it.

[jakevdp]

(providing good APIs for the new transforms is probably the biggest part of the work)