java - 从Python中的静态初始化器访问对象

Question

这是我之前的查询 Static initializer in Python 的延续我试图从它的一个属性中找到一个对象，就像在 java 中使用静态构造函数一样:

public class TestBuilder {
private String uid;
private String name;
private double speed;
private static ArrayList<TestBuilder> types = new ArrayList<TestBuilder>();
public static final TestBuilder SLEEPY;
public static final TestBuilder SPEEDY;

static {
    SLEEPY = new TestBuilder("1", "slow test", 500.00);
    SPEEDY = new TestBuilder("2", "fast test", 2000.00);
}

private TestBuilder(String uid, String name, double speed){
    this.uid = uid;
    this.name = name;
    this.speed = speed;
    types.add(this);
}

public static TestBuilder getBuilderFromName(String s){
    for (int i = 0; i < types.size(); i++){
        if (((TestBuilder) types.get(i)).name.equals(s)){
            return (TestBuilder) types.get(i);
        }
    }
    return null;
}

在 python 中我尝试过:

class TestBuilder:
    uid = str()
    name = str()
    speed = float()
    types = []

    def __init__(self, uid, name, speed):
        self.uid = uid
        self.name = name
        self.speed = speed
        self.types.append(self)

    @classmethod
    def lookupType(cls, name):
        for item in cls.types:
            if item.name == name:
                return cls

TestBuilder.SLEEPY = TestBuilder("1","slow test", 500.0)
TestBuilder.SPEEDY = TestBuilder("2","fast test", 2000.0)

然后在测试模块中:

class Tester(unittest.TestCase):
    def test_builder(self):
        dummy = TestBuilder
        ref = dummy.SPEEDY
        objfound = dummy.lookupType("slow test")
        logger.debug("--test_builder() name: "+objfound.name)

虽然在lookupType方法中找到了正确的对象，但在测试中访问时生成的classfound name属性为空。如何在给定其属性之一的情况下访问正确的 TestBuilder 对象？

Answer 1

您正在返回类，而不是您找到的实例:

@classmethod
def lookupType(cls, name):
    for item in cls.types:
        if item.name == name:
            return cls
            #      ^^^

退回商品:

return item

不要使用列表，而是使用字典注册您的类，这样您就可以简单地按名称查找它们:

class TestBuilder:
    types = {}

    def __init__(self, uid, name, speed):
        self.uid = uid
        self.name = name
        self.speed = speed
        self.types[name] = self

    @classmethod
    def lookupType(cls, name):
        return cls.types.get(name)

请注意，您的 uid = str() 和 speed = float() 行只是创 build 置为空字符串和 0.0 的类属性分别。这些行不会声明类型，Python 不会阻止您的代码在实例级别将不同的对象分配给这些属性。