为什么我无法删除（移除）Python中静态列表的明文'existing instance'？

Question

我的目的如下：如果创建了新实例，则必须将该实例添加到静态列表中。当创建的实例被删除时，它必须从静态列表中删除

并且终结器方法必须使用'del()'。

我遇到问题的 python 代码如下：

class Staff:
    staffs = []  # static customer list

    def __init__(self, name):
        self.name = name
        print("A staff is created!")

    def __del__(self):
        Staff.staffs.remove(self)
        print("A staff is deleted!")

if __name__ == '__main__':
    # create a staff
    Staff.staffs.append(Staff("Harry"))

    # delete a staff
    Staff.staffs[0].__del__()

错误如下：

异常被忽略：del at 0x0000028A3675EF70>

回溯（最后一次调用）： del 中的文件“(Path)\temp.py”，第 11 行 Staff.staffs.remove(自己)

ValueError: list.remove(x): x 不在列表中

而且我可以检查创建的实例是否存在于静态列表中，如下面的代码

def check(self):
    print("Length of Static List:", len(Staff.staffs))
    print("self", self)
    for a_staff in Staff.staffs:
        if a_staff == self:
            print("a_staff", a_staff)
    print()

结果：

静态列表长度：1

self <main.Staff 对象位于 0x000001FF7506CFD0>

a_staff <main.0x000001FF7506CFD0 处的工作人员对象>

实例的内存地址完全一样，但不知道为什么解释器说静态列表中没有实例。

当我运行类似的代码在Java时没有问题。

为什么会出现这个错误？

Answer 1

注意

class Staff:
    staffs = []  # static customer list

    def __init__(self, name):
        self.name = name
        print("A staff is created!")

    def delete(self):
        Staff.staffs.remove(self)
        print("A staff is deleted!")

if __name__ == '__main__':
    # create a staff
    Staff.staffs.append(Staff("Harry"))

    # delete a staff
    Staff.staffs[0].delete()

工作正常。我所做的只是重命名__del__删除。您可以尝试解释上面的 documentation 注释

Due to the precarious circumstances under which del() methods are invoked, exceptions that occur during their execution are ignored, and a warning is printed to sys.stderr instead.

以上引用解释了您的错误。但是，正如 other posts 大纲，__del__ 是一个

really low-level method which you don't need 99.9% of the time

所以只使用上面的代码就足够了，它会将您的实例标记为垃圾回收。

如果必须向 __del__ 命令添加其他内容，请尝试以下操作：

class Staff:
    staffs = []  # static customer list

    def __init__(self, name):
        self.name = name
        print("A staff is created!")

    def __del__(self):
        print("A staff is deleted!")

if __name__ == '__main__':
    # create a staff
    Staff.staffs.append(Staff("Harry"))

    print(f"The length of Staff before delete is: {len(Staff.staffs)}")
    # delete a staff
    del Staff.staffs[0]
    print(f"The length of Staff after delete is: {len(Staff.staffs)}")

这输出：

A staff is created!
The length of Staff before delete is: 1
A staff is deleted!
The length of Staff after delete is: 0

所以项目被删除，你的文字被打印出来，无一例外！

为什么我无法删除（移除）Python中静态列表的明文'existing instance'？

Why I can't delete (remove) the clearly 'existing instance' of the static list in Python?

python

static

instance