一个简单的递归函数可用于将一个实体（和任何引用对象）转换为可传递给的嵌套字典
simplejson：
import datetimeimport timeSIMPLE_TYPES = (int, long, float, bool, dict, basestring, list)def to_dict(model): output = {} for key, prop in model.properties().iteritems(): value = getattr(model, key) if value is None or isinstance(value, SIMPLE_TYPES): output[key] = value elif isinstance(value, datetime.date): # Convert date/datetime to MILLISECONDS-since-epoch (JS "new Date()"). ms = time.mktime(value.utctimetuple()) * 1000 ms += getattr(value, 'microseconds', 0) / 1000 output[key] = int(ms) elif isinstance(value, db.GeoPt): output[key] = {'lat': value.lat, 'lon': value.lon} elif isinstance(value, db.Model): output[key] = to_dict(value) else: raise ValueError('cannot enpre ' + repr(prop)) return output
