使用配置文件中的属性创建 class

Question

我正在尝试从配置文件动态创建 Python class（为简单起见，我在示例中使用字典）。我创建的属性我想设置为属性，因为我有验证功能，我想在设置属性时运行。

我有一个代码可以正常工作，但它有一些意想不到的结果。

def func(x):
    """ Example validation function. """
    if x < 0:
        raise ValueError

    return


config = {
    "x": {
        "type": int,
        "default": 0,
        "validate": func
    },
    "y": {
        "type": int,
        "default": 10,
        "validate": func
    },
    "z": {
        "type": str,
        "default": "bar",
        "validate": None
    }
}


def get_property(prop, validate):
    key = f"_{prop}"

    def get_(self):
        return exec(f"self.{key}")

    def set_(self, value):
        if validate is not None:
            validate(value)
        exec(f"self.{key} = value")

    def del_(self):
        exec(f"del self.{key}")

    return property(get_, set_, del_)


def get_Foo(**kwargs):
    class Foo:
        def __init__(self, **_kwargs):
            for k_, v_ in _kwargs.items():
                setattr(self, "_" + k_, None)

                if v_["type"] == str:
                    exec(f"self.{k_} = '{v_['default']}'")
                else:
                    exec(f"self.{k_} = {v_['default']}")

    # Add properties to Foo class
    for k, v in kwargs.items():
        prop_ = get_property(k, v["validate"])
        setattr(Foo, k, prop_)

    # Create Foo class and set defaults
    return Foo(**kwargs)


foo = get_Foo(**config)

现在测试时 'setter' 似乎在工作，但 'getter' 不工作，'deleter' 部分工作。

print(foo.x)  # prints None
print(foo._x) # prints 0
foo.x = 10
print(foo.x)  # prints None (getter not working)
print(foo._x) # prints 10  (setter works)
foo.x = -1    # raises error (validator in setter works)
del foo.x
print(foo.x)  # AttributeError: 'Foo' object has no attribute '_x' (del sort-of works?)

谁能解释一下结果？

Answer 1

感谢juanpa.arrivillaga；切换到 getattr、setattr、delattr 解决了这个问题。

解决方法如下：

def get_property(prop, validate):
    key = f"_{prop}"

    def get_(self):
        return getattr(self, key)

    def set_(self, value):
        if validate is not None:
            validate(value)
        setattr(self, key, value)

    def del_(self):
        delattr(self, key)

    return property(get_, set_, del_)


def get_Foo(**kwargs):
    class Foo:
        def __init__(self, **_kwargs):
            for k_, v_ in _kwargs.items():
                setattr(self, "_" + k_, None)
                setattr(self, k_, v_['default'])

    # Add properties to Foo class
    for k, v in kwargs.items():
        prop_ = get_property(k, v["validate"])
        setattr(Foo, k, prop_)

    # Create Foo class and set defaults
    return Foo(**kwargs)


foo = get_Foo(**config)

使用配置文件中的属性创建 class

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