human
Here's a good function header given the following:
I wrote the below code

    d2 = d.copy()
    def jsonify_bool(boolean_value):
        if boolean_value:
            return 'true'
        else:
            return 'false'
    for key in d2.keys():
        if isinstance(d2[key], bool):
            d2[key] = jsonify_bool(d2[key])
    return d2

What's a good function header?
assistant
#Here's a good function header.

def jsonify_dict(d):