python pandoc filter to add a base href/url to each image src

pandoc_filter_basehref.py

#!/usr/bin/env python3

from urllib.parse import urljoin
from pandocfilters import toJSONFilter, Image

BASEURL = "https://example.com"

def basehref(key, value, format, meta):
    if key == "Image":
        [[id, classes, attrs], children, [src, title]] = value
        src = urljoin(BASEURL, src)
        return Image([id, classes, attrs], children, [src, title])


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