`dump()` will fail if some key is an integer

Zeltserj

Running: ``` from yacs.config import CfgNode as CN cfg = CN() cfg["MYKEY"] = CN() cfg.MYKEY[1] = "a_sub_value" print(cfg.dump()) ``` Gives: ``` Traceback (most recent call last): File "/Users/zeltserj/yacs/example/main.py", line 5, in <module> print(cfg.dump()) File "/Users/zeltserj/yacs/yacs/config.py", line 206, in dump self_as_dict = convert_to_dict(self, []) File "/Users/zeltserj/yacs/yacs/config.py", line 203, in convert_to_dict cfg_dict[k] = convert_to_dict(v, key_list + [k]) File "/Users/zeltserj/yacs/yacs/config.py", line 203, in convert_to_dict cfg_dict[k] = convert_to_dict(v, key_list + [k]) File "/Users/zeltserj/yacs/yacs/config.py", line 196, in convert_to_dict ".".join(key_list), type(cfg_node), _VALID_TYPES TypeError: sequence item 1: expected str instance, int found ``` running with "1" instead, works fine.

luowyang

It seems that ".".join(key_list) does not accept integer as list element. The same is observed when the config is read from file which contains integer as key. Maybe it should be made clear that pure numbers should not be used as keys, or to parse integer keys as strings.