Compress json with lots of small strings

compress_json.py

def compress_json(obj):
    '''
    Performs string interning for non-compile time small strings.
    '''
    if isinstance(obj, (str, unicode)):
        return intern(str(obj))
    elif isinstance(obj, dict):
        return { intern(str(k)) : compress_json(v) for k, v in obj.iteritems() }
    elif hasattr(obj, '__iter__') and not isinstance(obj, (str, bytes, bytearray)):
        return [ compress_json(e) for e in obj ]
    else:
        return obj