判断python 列表/字典深层key是否存在的方法

import types

def json_get(json, l_key, default):
ret = json
for k in l_key:
if type(k) is types.IntType:
if k < 0 : return default
if not (type(ret) is types.ListType): return default
if len(ret) <= k: return default
elif type(k) is types.StringType:
if not (type(ret) is types.DictType): return default
if not ret.has_key(k): return default
else:
return default
ret = ret[k]

return ret

d = {'a':[{'objec':{'url':'http...'}}], b:'11'}
json_get(d, ['a', 0, 'objec', 'url'], 'err')  # 'http...'
json_get(d, ['b'], 'err') # err
json_get(d, ['a', '0', 'object', 'url'], 'not') # not