nbconvert: Failure in specifying user filter

[jakevdp]

I'm attempting to override the highlight filter for the notebook exporters. The following snippet leads to a failure:

from IPython.nbconvert.filters.highlight import _pygment_highlight
from pygments.formatters import HtmlFormatter
from IPython.nbformat import current as nbformat

from IPython.nbconvert.exporters import FullHtmlExporter


def my_highlight(source, language='ipython'):
    formatter = HtmlFormatter()
    return _pygment_highlight(source, formatter, language)

infile = 'test_notebook.ipynb'
outfile = 'test_notebook.html'

notebook = open(infile).read()
notebook_json = nbformat.reads_json(notebook)

exportHtml = FullHtmlExporter(filters={'highlight':my_highlight})
(body,resources) = exportHtml.from_notebook_node(notebook_json)

open(outfile, 'w').write(body)

This is the traceback:

Traceback (most recent call last):
  File "fail_case.py", line 19, in <module>
    exportHtml = FullHtmlExporter(filters={'highlight':my_highlight})
  File "/Users/jakevdp/Opensource/ipython/IPython/nbconvert/exporters/exporter.py", line 163, in __init__
    if issubclass(user_filter, MetaHasTraits):
TypeError: issubclass() arg 1 must be a class

Perhaps testing for isinstance(user_filter, type) would fix this -- though I'm not sure.

[jakevdp]

It looks like the offending line could be replaced with self.register_filter(key, user_filter). I tried this, and got a long and involved traceback. Note that the my_highlight function is identical to the highlight function that it is replacing: are user filters handled differently than default filters?

[Carreau]

Fixed by #3512