from collections import defaultdict

create_dict = lambda: defaultdict(create_dict)

def auto_defaultidct(keys, d=create_dict()):
    buffer = ''

    for i, item in enumerate(range(len(keys))):
        if i == 0:
            buffer = 'd'

        buffer += f'[keys[{item}]]'

    buffer += ' = create_dict()'

    exec(buffer, None, locals())

    return d

auto_defaultidct('this function call will create a defaultdict that expands for every word in this sentece'.split(' '))