recursive operation on key

recursive_op_key.py

def lower(obj):
    return obj.lower()

def lower_dict(obj):
    return _recursive_key_op(obj, lower)

def _recursive_key_op(obj, op=None):
    if isinstance(obj, dict):
        return {op(k): _recursive_key_op(v, op) for k, v in obj.items()}
    elif isinstance(obj, (list, set, tuple)):
        t = type(obj)
        return t(_recursive_key_op(o, op) for o in obj)
    elif isinstance(obj, str):
        return op(obj)
    else:
        return obj