Question

class Class():
    id_list = []

    def __init__(self, name, id):
        self.name = name
        self.id = id
        Class.id_list.append(self.id)

class1 = Class("Bob", 0)
class2 = Class("John", 1)

我想要做的是查看每个Class实例的ID，如果它与某个ID匹配，那么它会告诉我类的名称，这可能吗？例如：如果我正在寻找“John”，我会寻找ID号1

Answer 1

如果您只在id类变量中存储每个实例的id_list值，那么就没有简单的方法来获取相应的名称。但是，如果您可以更改逻辑以在列表中存储对整个实例的引用而不是id，那么您就可以在其上查找所需的任何属性。如果id进行查找很常见，那么您可能希望使用字典而不是列表来获得更快的查找（尽管id值总是从0开始并且每次增加1，您就可以在O(1)时间内为列表编制索引。

尝试这样的事情：

class Class:
    instances = []

    def __init__(self, name): # no id arg needed
        self.name = name  # your code probably shouldn't have quotation marks around "name"
        self.id = len(self.instances) # automatically use the next available id value
        self.instances.append(self) # append a reference to the whole instance to the list

    @classmethod
    def lookup_class_name_by_id(cls, id):
        if 0 <= id < len(cls.instances):
            return cls.instances[id].name
        raise ValueError("Invalid ID {}".format(id))

Answer 2

如果我理解正确，你想通过id函数创建一个搜索，以便id链接到一个实例，你可以为它创建一个字典，键作为id，值作为实例。

class Class():
    id_list = {} # id_list will be a dict instead

    def __init__(self, name, id):
        self.name = name # no quotation marks...
        self.id = id
        Class.id_list[self.id] = self # save the id as key and self as he value

    @classmethod
    def search_by_id(cls, id):
        try:
            return cls.id_list[id] # return the instance with the id 
        except KeyError: # error check for if id does not exist
            raise KeyError("No user with id %s" % str(id))

class1 = Class("Bob", 0)
class2 = Class("John", 1)
print(Class.search_by_id(0).name) # prints Bob
print(Class.search_by_id(1).name) # prints John
print(Class.search_by_id(2).name) # prints raised a KeyError since id 2 doesn't exist yet: KeyError: 'No user with id 2'

Answer 3

如果您希望每次为某个人实例时他们都有新ID，您可以这样做：

class MyClass():
    ids = 0
    id_list = {}

    def __init__(self, name):
        self.name = "name"
        MyClass.ids += 1
        self.myId = MyClass.ids
        MyClass.id_list[self.myId] = self

   def search_by_id(id):
      return MyClass.id_list[id]

bob = MyClass("bob")
kyle = MyClass("kyle")
print(bob.myId)
print(kyle.myId)
print(MyClass.search_by_id(2).name)

>1
>2
>kyle

如何通过类变量查找类的特定实例？

3 个答案: