类型错误：“可调用[[VarArg(Any)，KwArg(Any)]，Any]”没有属性*

Question

我正在定义一个类，如果没有声明color实例属性，则根据接收的调用数自动设置它。

在下面，您可以看到一个最小的工作示例：

from typing import Callable
import itertools
from plotly.express import colors as px_colors
COLOR_LIST = px_colors.qualitative.Alphabet

# Decorator
def color_setter(func: Callable):
    """Counts how many times `~MyClass` has been called and sets the
    instance color accordingly.

    Parameters
    ----------
    func : Callable

    Returns
    -------
    Callable
    """

    def wrapper(*args, **kwargs):
        wrapper.calls += 1
        wrapper.color = next(wrapper.cycle_color_list)
        # print(f'wrapper called {wrapper.calls} times')
        return func(*args, **kwargs)
    
    wrapper.calls = 0  # Adding # type: ignore here suppresses
                       # the error, but it is not a solution...
    wrapper.cycle_color_list = itertools.cycle(COLOR_LIST)  # same here

    return wrapper

@color_setter
def _set_color(color: str) -> tuple:
    """Sets MyClass color and id.

    Parameters
    ----------
    color : str
        Color variable, can be RGBA or HEX string format.

    Returns
    -------
    tuple
        MyClass color and call id
    """
    if color is None:
        color = _set_color.color
    my_id = _set_color.calls
    return color, my_id


class MyClass():
    """Example class.
    """

    def __init__(
        self,
        color: str = None,
    ) -> None:
        """Define MyClass.

        Parameters
        ----------
        color : str, optional
            RGBS or HEX string for color, by default None
        """
        self.color, self.id = _set_color(color)

代码的行为与预期相同，但mypy返回以下两个错误，我无法解决这些错误。

example.py:26: error: "Callable[[VarArg(Any), KwArg(Any)], Any]" has no attribute "calls"
        wrapper.calls = 0
        ^
example.py:27: error: "Callable[[VarArg(Any), KwArg(Any)], Any]" has no attribute "cycle_color_list"
        wrapper.cycle_color_list = itertools.cycle(COLOR_LIST)
        ^
Found 2 errors in 1 file (checked 1 source file)

Answer 1

Mypy抱怨功能属性没有被正确输入。

定义一个包装函数，它的类型为Callable[[VarArg(Any), KwArg(Any)], Any]。此类型不附带属性calls和color。因此，访问它会导致属性错误。

from typing import Callable, Optional

# Decorator
def color_setter_alt(func: Callable):
    """Counts how many times `~MyClass` has been called and sets the
    instance color accordingly.

    Parameters
    ----------
    func : Callable

    Returns
    -------
    Callable
    """

    class Wrapper:
        color: Optional[str]

        def __init__(self):
            # Wrapper is callable because it has the `__call__` method.
            # Not being a plain function allows you to explicitly define the function attributes
            self.calls = 0
            self.cycle_color_list = itertools.cycle(COLOR_LIST)

        def __call__(self, *args, **kwargs):
            self.calls += 1
            self.color = next(self.cycle_color_list)
            # print(f'wrapper called {wrapper.calls} times')
            return func(*args, **kwargs)

    return Wrapper()

另一个解决办法是使用setattr和getattr。

# Decorator
def color_setter(func: Callable):
    """Counts how many times `~MyClass` has been called and sets the
    instance color accordingly.

    Parameters
    ----------
    func : Callable

    Returns
    -------
    Callable
    """

    def wrapper(*args, **kwargs):
        setattr(wrapper, "calls", getattr(wrapper, "calls") + 1)
        setattr(wrapper, "color", next(getattr(wrapper, "cycle_color_list")))
        # print(f'wrapper called {wrapper.calls} times')
        return func(*args, **kwargs)
    
    setattr(wrapper, "calls", 0) 
    setattr(wrapper, "cycle_color_list", itertools.cycle(COLOR_LIST))

    return wrapper

这种方法的优点是，您可以在以后对附加属性进行猴子修补，而不必修改原始函数。但缺点是它不能为您提供输入提示。