python - 在 Python 中创建列表属性

Question

我开始使用 Python 3 进行 OOP，我发现属性的概念非常有趣。

我需要封装一个私有(private)列表，但是如何将这种范例用于列表？

这是我天真的尝试:

class Foo:
    """ Naive try to create a list property.. and obvious fail """

    def __init__(self, list):
        self._list = list

    def _get_list(self, i):
        print("Accessed element {}".format(i))
        return self._list[i]

    def _set_list(self, i, new):
        print("Set element {} to {}".format(i, new))
        self._list[i] = new

    list = property(_get_list, _set_list)

当我尝试以下代码时，这不会按预期运行，甚至使 python 崩溃。这是我希望 Foo 展示的虚构行为:

>>> f = Foo([1, 2, 3])
>>> f.list
[1, 2, 3]
>>> f.list[1]
Accessed element 1
2
>>> f.list[1] = 12
Set element 1 to 12
>>> f.list
[1, 12, 3]

Answer 1

import collections


class PrivateList(collections.MutableSequence):
    def __init__(self, initial=None):
        self._list = initial or []

    def __repr__(self):
        return repr(self._list)

    def __getitem__(self, item):
        print("Accessed element {}".format(item))
        return self._list[item]

    def __setitem__(self, key, value):
        print("Set element {} to {}".format(key, value))
        self._list[key] = value

    def __delitem__(self, key):
        print("Deleting element {}".format(key))
        del self._list[key]

    def __len__(self):
        print("Getting length")
        return len(self._list)

    def insert(self, index, item):
        print("Inserting item {} at {}".format(item, index))
        self._list.insert(index, item)


class Foo(object):
    def __init__(self, a_list):
        self.list = PrivateList(a_list)

然后运行这个:

foo = Foo([1,2,3])
print(foo.list)
print(foo.list[1])
foo.list[1] = 12
print(foo.list)

输出:

[1, 2, 3]
Accessed element 1
2
Set element 1 to 12
[1, 12, 3]