调用属性方法的好方法

Question

想象一下下面的代码（单独看完全没用）：

# define a property with additional methods
class P(property):
    def __init__(self, name):
        property.__init__(self, 
            fget=lambda self: self._get(name),
            fset=lambda self, v: self._set(name, v))
        self._name = name

    def some_fn(self):
        print('name: ' + self._name)

# define a class with two 'enhanced' properties
class C:
    p1 = P('p1')
    p2 = P('p2')

    def __init__(self):
        self._values = {}

    def _get(self, name):
        return self._values[name]

    def _set(self, name, v):
        self._values[name] = v

c = C()

c.p1 = 5
c.p2 = c.p1

print(c.p1, c.p2)

我只是用两个properties 创建了一个类C，它们有一个额外的方法some_fn()。

现在的问题是：你不能通过写c.p1.some_fn() 轻松调用some_fn()，因为你会先评估c.p1，这会导致一些值不再提供该方法。

我试图找到一些在certain property 的上下文中调用some_fn 的变通方法/方法，这不是它的价值，但我还不开心。

我的目标很简单：

• 我希望能够在没有样板的情况下读取/分配属性： c.p1 = c.p2 而不是 c.p1.set(c.p2.get())

• 我调用额外方法/函数的方式必须易于读/写

• 我想编写可以被pylint、mypy等静态验证的代码，所以some_fn('c.p1') is not an option because it can't be checked whether 'c.p1' is a valid attribute of an existing objectc`。

• some_fn 不必必须是一种方法。它可以是一个函数或任何其他在属性上下文中请求功能的方式

• 我什至不需要真实 properties。任何其他写s.th的方式。 像 c.p1 == c.p2 一样（例如使用 __getattr__/__setattr__）也可以，只要 get/set 操作仍然可跟踪。

我收集了一些代码来说明我在说什么：

# ==== What I want to do ==============
c.p1.some_fn()              #  <-- this is what I want to write but
                            #      it's invalid since it evaluates to
                            #      5.some_fn()

some_fn(c.p1)               #  <-- something like this looks OK, too but
                            #      it evalueates to some_fn(5) (useless)

# ==== These are options that came to mind but I'm not happy with ======

getattr(C, 'p1').some_fn()  #  <-- this works but it is ugly

some_fn("c.p1")             #  <-- this is possible, too but I can't 
                            #      check integrity statically (pylint/mypy)

c.p1.value = c.p2.value     #  <-- this is a valid approach but it 
c.p1.some_fn()              #      increases

some_fn(c.p1)  # (again)    #  <-- This can acutally work if you `inspect`
                            #      the call stack inside `C._get()` but 
                            #      it's black magic and incredibly slow

with some_fn():             #  <-- this can work when `some_fn` changes 
    c.p1                    #      some global state which get's evaluated
                            #      inside `C._get()`

Answer 1

我的目标很简单：我希望能够在没有样板的情况下读取/分配属性：c.p1 = c.p2

如果这是这里的目标，那听起来您误解了属性，因为它们已经像那样工作了。

class C(object):
    @property
    def p1(self):
        # get value
    @p1.setter
    def p1(self, val):
        # set value

    @property
    def p2(self):
        # get value
    @p2.setter
    def p2(self, val):
        # set value

如果你有一个对象c = C()，你可以做c.p1 = c.p2，它就可以工作。将更多方法粘贴到 property 对象上是错误的方法。

---

如果你真的想将方法粘贴到属性上，请通过类检索属性：

C.p1.some_fn()