docs: def compare_dicts(d1, d2):
      """
      Returns a diff string of the two dicts.
      """
      a = json.dumps(d1, indent=4, sort_keys=True)
      b = json.dumps(d2, indent=4, sort_keys=True)
      # stolen from cpython
      # https://github.com/python/cpython/blob/01fd68752e2d2d0a5f90ae8944ca35df0a5ddeaa/Lib/unittest/case.py#L1091
      diff = ('\n' + '\n'.join(difflib.ndiff(
                     a.splitlines(),
                     b.splitlines())))
      return diff