python - 是否可以用装饰器修改类

Question

我正在用 python 编写一个类，用于一些设置，如下所示:

class _CanvasSettings:
    def __init__(self, **kwargs):
        super().__init__()
        self._size_x = _int(kwargs, 'size_x', 320)
        self._size_y = _int(kwargs, 'size_y', 240)
        self._lock_ratio = _bool(kwargs'lock_ratio', True)

    def get_size_x_var(self):
        return self._size_x
    def _get_size_x(self):
        return self._size_x.get()
    def _set_size_x(self, value):
        self._size_x.set(value)
    size_x = property(_get_size_x, _set_size_x)

    def get_size_y_var(self):
        return self._size_y
    def _get_size_y(self):
        return self._size_y.get()
    def _set_size_y(self, value):
        self._size_y.set(value)
    size_y = property(_get_size_y, _set_size_y)

    def get_lock_ratio_var(self):
        return self._lock_ratio
    def _get_lock_ratio(self):
        return self._lock_ratio.get()
    def _set_lock_ratio(self, value):
        self._lock_ratio.set(value)
    lock_ratio = property(_get_lock_ratio, _set_lock_ratio)

如你所见，我添加了 block :

    def get_something_var(self):
        return self._something
    def _get_something(self):
        return self._something.get()
    def _set_something(self, value):
        self._something.set(value)
    something = property(_get_something, _set_something)

对于每一个设置。
是否可以使用装饰器自动执行此任务？

我想这样做(伪代码):

def my_settings_class(cls):
    result = cls
    for field in cls:
        result.add_getter_setter_and_property( field )
    return result

@my_settings_class
class _CanvasSettings:
    def __init__(self, **kwargs):
        super().__init__()
        self._size_x = _int(kwargs, 'size_x', 320)
        self._size_y = _int(kwargs, 'size_y', 240)
        self._lock_ratio = _bool(kwargs'lock_ratio', True)

# Done !

这可能吗？
如果是，如何？
如何实现add_getter_setter_and_property()方法？

<小时/>

编辑:
这里有一个非常相似的问题:Python Class Decorator
从那里的答案中，我怀疑有可能实现我所要求的目标，但是您能给我一些有关如何实现 add_getter_setter_and_property() 函数/方法的线索吗？

<小时/>

注意:
如果字符串(例如“size_x”)存在或来自默认值，则 _int()、_bool() 函数仅从 kwargs 返回 8 个 tkinter Int/Bool-var值(例如 320)。

<小时/>

我的最终解决方案: 我想我已经找到了一个非常好的解决方案。我只需添加一次设置名称，这在我看来非常棒:-)

import tkinter as tk

def _add_var_getter_property(cls, attr):
    """ this function is used in the settings_class decorator to add a
    getter for the tk-stringvar and a read/write property to the class.
    cls:  is the class where the attributes are added.
    attr: is the name of the property and for the get_XYZ_var() method.
    """
    field = '_' + attr
    setattr(cls, 'get_{}_var'.format(attr), lambda self: getattr(self, field))
    setattr(cls, attr,
            property(lambda self: getattr(self, field).get(),
                     lambda self, value: getattr(self, field).set(value)))

def settings_class(cls):
    """ this is the decorator function for SettingsBase subclasses.
    it adds getters for the tk-stringvars and properties. it reads the
    names described in the class-variable _SETTINGS.
    """
    for name in cls._SETTINGS:
        _add_var_getter_property(cls, name)
    return cls


class SettingsBase:
    """ this is the base class for a settings class. it automatically
    adds fields to the class described in the class variable _SETTINGS.
    when you subclass SettingsBase you should overwrite _SETTINGS.
    a minimal example could look like this:

      @settings_class
      class MySettings(SettingsBase):
          _SETTINGS = {
              'x': 42,
              'y': 23}

    this would result in a class with a _x tk-intvar and a _y tk-doublevar
    field with the getters get_x_var() and get_y_var() and the properties
    x and y.
    """

    _SETTINGS = {}

    def __init__(self, **kwargs):
        """ creates the fields described in _SETTINGS and initialize
        eighter from the kwargs or from the default values
        """
        super().__init__()
        fields = self._SETTINGS.copy()
        if kwargs:
            for key in kwargs:
                if key in fields:
                    typ = type(fields[key])
                    fields[key] = typ(kwargs[key])
                else:
                    raise KeyError(key)
        for key in fields:
            value = fields[key]
            typ = type(value)
            name = '_' + key
            if typ is int:
                var = tk.IntVar()
            elif typ is str:
                var = tk.StringVar()
            elif typ is bool:
                var = tk.BooleanVar()
            elif typ is float:
                var = tk.DoubleVar()
            else:
                raise TypeError(typ)
            var.set(value)
            setattr(self, name, var)

之后我的设置类看起来就像这样:

@settings_class
class _CanvasSettings(SettingsBase):

    _SETTINGS = {
        'size_x': 320,
        'size_y': 240,
        'lock_ratio': True
        }

Answer 1

使用setattr将函数和属性绑定(bind)为类对象的属性当然可以做你想做的事情:

def add_getter_setter_property(cls, attrib_name):
    escaped_name = "_" + attrib_name
    setattr(cls, "get_{}_var".format(attrib_name),
            lambda self: getattr(self, escaped_name))
    setattr(cls, attrib_name,
            property(lambda self: getattr(self, escaped_name).get()
                     lambda self, value: getattr(self, escaped_name).set(value)))

这里我跳过为 property 使用的 getter 和 setter 方法命名。如果您确实愿意，可以将它们添加到类(class)中，但我认为这可能没有必要。

棘手的一点实际上可能是找到您需要将其应用到哪些属性名称。与您的示例不同，您无法迭代类对象来获取其属性。

最简单的解决方案(从实现的角度来看)是要求类在类变量中指定名称:

def my_settings_class(cls):
    for field in cls._settings_vars:
        add_getter_setter_and_property(cls, field)
    return cls

@my_settings_class
class _CanvasSettings:
    _settings_vars = ["size_x", "size_y", "lock_ratio"]
    def __init__(self, **kwargs):
        super().__init__()
        self._size_x = _int(kwargs, 'size_x', 320)
        self._size_y = _int(kwargs, 'size_y', 240)
        self._lock_ratio = _bool(kwargs, 'lock_ratio', True)

更用户友好的方法可能会使用 dir 或 vars 来检查类变量并挑选出需要自动包装的变量。您可以使用 isinstance 来检查值是否具有特定类型，或者在属性名称中查找特定模式。我不知道什么最适合您的具体用途，所以我将其留给您。