[英]python - why is read-only property writable?
I am trying to define a class with a read-only property in a Python; 我试图在Python中定义一个只读属性的类; I followed Python documentation and came up with the following code:
我按照Python文档编写了以下代码:
#!/usr/bin/python
class Test:
def __init__(self, init_str):
self._prop = init_str
@property
def prop(self):
return self._prop
t = Test("Init")
print t.prop
t.prop = "Re-Init"
print t.prop
Now when I try to execute the code though I am expecting error/exception I see it getting executed normally: 现在当我尝试执行代码虽然我期待错误/异常时,我看到它正常执行:
$ ./python_prop_test
Init
Re-Init
My Python version is 2.7.2. 我的Python版本是2.7.2。 What I am seeing, is it expected?
我所看到的,是否有望? How do make sure a property is not settable?
如何确保房产不可设置?
For this to work as you expect, Test
needs to be a new-style class: 为了使其按预期工作,
Test
需要是一个新式的类:
class Test(object):
^^^^^^^^
This is hinted at in the documentation for property()
: 这在
property()
的文档中暗示:
Return a property attribute for new-style classes (classes that derive from
object
).返回新样式类的属性属性(从
object
派生的类)。
When I turn Test
into a new-style class, and attempt to change prop
, I get an exception: 当我将
Test
变成一个新式的类,并试图改变prop
,我得到一个例外:
In [28]: t.prop='Re-Init'
AttributeError: can't set attribute
To use properties you must use new-style classes. 要使用属性,必须使用新式类。 To use new-style classes in Python 2 you must inherit from
object
. 要在Python 2中使用新式类,必须从
object
继承。 Change your class def to class Test(object)
. 将类def更改为
class Test(object)
。
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