A pandoc filter for converting jupytext or similar markdown to a codebraid notebook

cbnb.filter.py

#!/usr/bin/env python

"""A Pandoc filter to convert jupytext (or similar)
markdown to a codebraid "notebook".
"""

from pandocfilters import toJSONFilter, CodeBlock


def get_jupyter_kernel(data):
    keys = [
        'jupyter',
        'c',
        'kernelspec',
        'c',
        'name',
    ]
    
    for key in keys:
        data = data.get(key)
        if isinstance(data, dict):
            pass
        else:
            return None
    data = data['c']
    
    while True:
        if isinstance(data, dict):
            data = data['c']
        elif isinstance(data, list):
            data = data[0]
        else:
            return data

        
class CBNoteBookFilter(object):

    def __init__(self):
    
        self.first_code_block = True
        
    def __call__(self, key, value, format, meta):
        """replace code block classes with '.cb.nb' and add
        jupyter kernelspec to first code block if a kerel 
        is specified in metadata.
        """
        
        if key == 'CodeBlock':
            
            [[ident, classes, keyvals], code] = value

            # add notebook class if language specified
            if len(classes) > 0:
                classes = [classes[0], 'cb.nb']

            # look for a jupyter kernel if this is the first block
            if self.first_code_block:
                kernel = get_jupyter_kernel(meta)
                if kernel:
                    keyvals.append(['jupyter_kernel', kernel])
                self.first_code_block = False
            
            return CodeBlock([ident, classes, keyvals], code)


if __name__ == "__main__":
    toJSONFilter(CBNoteBookFilter())