conn.get_dict('key') is giving me a error

I am using your example 
dictionary = {
    'a': {
        'key': 'a_value'
    },
    'another': {
        'k': 'another_value'
    }
}

conn.put_dict(dictionary)
conn.get_dict() ---> This works and gives me all the dictionary
conn.get_dict('a') ==== > This gives me an error

 
 raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 404: Not Found

