python - 为什么只读属性可写? [英] python - why is read-only property writable?

问题描述

我试图在 Python 中定义一个具有只读属性的类；我遵循了 Python 文档并提出了以下代码:

I am trying to define a class with a read-only property in a Python; I followed Python documentation and came up with the following code:

#!/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

现在，当我尝试执行代码时，虽然我期待错误/异常，但我看到它正常执行:

Now when I try to execute the code though I am expecting error/exception I see it getting executed normally:

$ ./python_prop_test 
Init
Re-Init

我的 Python 版本是 2.7.2.我所看到的，是预期的吗?如何确保属性不可设置?

My Python version is 2.7.2. What I am seeing, is it expected? How do make sure a property is not settable?

推荐答案

为了让这个如你所愿，Test 需要是一个新风格的类:

For this to work as you expect, Test needs to be a new-style class:

class Test(object):
          ^^^^^^^^

这在 property() 文档:

返回新样式类(派生自object的类)的属性属性.

Return a property attribute for new-style classes (classes that derive from object).

当我把 Test 变成一个新样式的类，并试图改变 prop 时，我得到一个异常:

When I turn Test into a new-style class, and attempt to change prop, I get an exception:

In [28]: t.prop='Re-Init'

AttributeError: can't set attribute

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