Question

我正在编写一个简单的ORM，它要求我覆盖子类中的方法。根据上下文，我或者期望通过类方法或实例方法访问模型，因此我不能简单地覆盖它们。我相信这段代码很好地描述了这个问题：

import React, { Component } from 'react';
import { Route, Switch, Redirect, Link } from 'react-router-dom';
import { BrowserRouter, withRouter } from 'react-router-dom';
import { connect } from 'react-redux';
import { bindActionCreators } from 'redux';
import * as actionCreators from '../actions/actionCreators';

class App extends Component {
    constructor() {
        super();
    };

    render() {
        return (
            <div>
                <a href="/"> main</a>
                &nbsp;&nbsp;&nbsp;&nbsp;
                <a href='/info'>info</a>
                <Switch>
                    <Route exact path="/" render={() => <h1>kawaii world</h1>} />
                    <Route exact path="/info" render={() => <h1>v kawaii world ;)</h1>} />
                </Switch>
            </div>
        );
    };
};

function mapStateToProps(state) {
    return {
        count: state.count
    };
};

function mapDispatchToProps(dispatch) {
    return bindActionCreators(actionCreators, dispatch);
};

export default withRouter(connect(mapStateToProps, mapDispatchToProps)(App));

Answer 1

您的B.key_fn确实会被调用。但是你的load_all会返回一个生成器，因为你让它yield from db_fetch_prefix。您可以在最后运行print(B.load_all())来检查此问题。输出将是：

python .\clsss.py
<generator object A.load_all at 0x0521A330>

使用yield from我不知道您想要达到的目标。但是可以在子类中显示覆盖类方法的示例是：

class A:
    @classmethod
    def key_fn(cls, id):
        raise NotImplementedError('')

    @classmethod
    def load_all(cls):
        return cls.key_fn('foo')

class B(A):
    @classmethod
    def key_fn(cls, id):
        return f'/keys/{id}'

print(B.load_all())  # prints "/keys/foo"

疯狂地猜测您要将key_fn应用于您的生成器db_fetch_prefix（下面缩写为fetch）所产生的每个项目，下面的代码显示B.key_fn将是也用于发电机。

def fetch(callback):
    for i in range(5):  # fake DB fetch
        yield callback(i)

class A:
    @classmethod
    def key_fn(cls, id):
        raise NotImplementedError('')

    @classmethod
    def load_all(cls):
        yield from fetch(cls.key_fn)

class B(A):
    @classmethod
    def key_fn(cls, id):
        return f'/keys/{id}'

print(list(B.load_all()))  # prints ['/keys/0', '/keys/1', '/keys/2', '/keys/3', '/keys/4']

Python覆盖了孩子们的classmethod

1 个答案: