AppEngine:我可以编写一个动态属性(db.Expando),其名称是在运行时选择的吗？

Question

如果我有一个从db.Expando派生的实体,我可以通过为新属性赋值来编写Dynamic属性,例如在这个例子中为"y":

class MyEntity(db.Expando):  
  x = db.IntegerProperty()  

my_entity = MyEntity(x=1)  
my_entity.y = 2  

但是假设我在变量中有动态属性的名称...我如何(1)读取和写入它,以及(2)检查实体的实例中是否存在动态变量？例如

class MyEntity(db.Expando):  
  x = db.IntegerProperty()  

my_entity = MyEntity(x=1)  
# choose a var name:  
var_name = "z"  
# assign a value to the Dynamic variable whose name is in var_name:  
my_entity.property_by_name[var_name] = 2  
# also, check if such a property esists  
if my_entity.property_exists(var_name):  
  # read the value of the Dynamic property whose name is in var_name
  print my_entity.property_by_name[var_name]  

谢谢...

Answer 1

是的你可以.您只需在实体上设置属性:

some_name = 'wee'
setattr(my_entity, some_name, 'value')
print getattr(my_entity, some_name)
my_entity.put()

setattr并且getattr是Python的内置函数,用于在对象上设置/获取具有任意名称的属性.