C# 通用 List<T> 的 Python 等效项

Question

我正在创建一个简单的 GUI 程序来管理优先级。

我已经成功地添加了将项目添加到列表框的功能。现在我想将该项目添加到 C# 中称为 List<> 的内容中。Python中存在这样的东西吗？

例如，在 C# 中，要将项目添加到列表视图，我首先要创建：

List<Priority> priorities = new List<Priority>();

...然后创建以下方法：

void Add()
{
    if (listView1.SelectedItems.Count > 0)
    {
        MessageBox.Show("Please make sure you have no priorities selected!", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
    else if (txt_Priority.ReadOnly == true) { MessageBox.Show("Please make sure you refresh fields first!", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Information); }
    else
    {
        if ((txt_Priority.Text.Trim().Length == 0)) { MessageBox.Show("Please enter the word!", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Information); }
        else
        {
            Priority p = new Priority();
            p.Subject = txt_Priority.Text;

            if (priorities.Find(x => x.Subject == p.Subject) == null)
            {
                priorities.Add(p);
                listView1.Items.Add(p.Subject);
            }
            else
            {
                MessageBox.Show("That priority already exists in your program!");
            }
            ClearAll();
            Sync();
            Count();
        }
    }
    SaveAll();

}

Answer 1

类型提示

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从 Python 3.5 开始，可以添加类型提示。结合数据类(Python 3.7+) 和泛型集合(Python 3.9+)，您可以编写：

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from dataclasses import dataclass\n\n\n@dataclass\nclass Priority:\n    """Basic example class"""\n    name: str\n    level: int = 1\n\n\nfoo = Priority("foo")\nbar = Priority("bar", 2)\n\npriorities: list[Priority] = [foo, bar]\n\nprint(priorities)\n# [Priority(name=\'foo\', level=1), Priority(name=\'bar\', level=2)]\nprint(sorted(priorities, key= lambda p: p.name))\n# [Priority(name=\'bar\', level=2), Priority(name=\'foo\', level=1)]\n\nbaz = "Not a priority"\npriorities.append(baz) # <- Your IDE will probably complain\n\nprint(priorities)\n# [Priority(name=\'foo\', level=1), Priority(name=\'bar\', level=2), \'Not a priority\']\n

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在 Python 3.5 中，代码如下所示：

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from typing import List\n\n\nclass Priority:\n    """Basic example class"""\n    def __init__(self, name: str, level: int = 1):\n        self.name = name\n        self.level = level\n\n    def __str__(self):\n        return \'%s (%d)\' % (self.name, self.level)\n\n    def __repr__(self):\n        return str(self)\n\n\nfoo = Priority("foo")\nbar = Priority("bar", 2)\n\npriorities: List[Priority] = [foo, bar]\n\nprint(priorities)\n# [foo (1), bar (2)]\nprint(sorted(priorities, key=lambda p: p.name))\n# [bar (2), foo (1)]\n\nbaz = "Not a priority"\npriorities.append(baz) # <- Your IDE will probably complain\n\nprint(priorities)\n# [foo (1), bar (2), \'Not a priority\']\n

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请注意，类型提示是可选的，即使附加时存在类型不匹配，上述代码也将正常运行baz。

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您可以使用以下命令显式检查错误mypy：

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\xe2\x9d\xaf mypy priorities.py\npriorities.py:22: error: Argument 1 to "append" of "list" has incompatible type "str"; expected "Priority"\nFound 1 error in 1 file (checked 1 source file)\n

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动态语言

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即使现在有类型提示，Python 仍然保持动态，并且类型提示是完全可选的：

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>>> my_generic_list = []\n>>> my_generic_list.append(3)\n>>> my_generic_list.append("string")\n>>> my_generic_list.append([\'another list\'])\n>>> my_generic_list\n[3, \'string\', [\'another list\']]\n

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在将任何对象附加到现有列表之前，您不必定义任何内容。

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Python 使用鸭子类型。如果您迭代列表并对每个元素调用方法，则需要确保元素理解该方法。

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所以如果你想要相当于：

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List<Priority> priorities\n

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您只需要初始化一个列表并确保只Priority向其中添加实例。就是这样！

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