Inflate a flattened dictionary

inflate.py

def inflate(d, sep="_"):
    items = dict()
    for k, v in d.items():
        keys = k.split(sep)
        sub_items = items
        for ki in keys[:-1]:
            try:
                sub_items = sub_items[ki]
            except KeyError:
                sub_items[ki] = dict()
                sub_items = sub_items[ki]
            
        sub_items[keys[-1]] = v

    return items