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Oleksii's questions

Martin Hope
Oleksii
Asked: 2020-04-25 16:01:57 +0000 UTC
  • 1

我需要创建一个像 Singleton 一样工作的类，并且应该从基类继承。可以有几个类，如 MyClass。

最后，我想出了以下解决方案：

import random


class Singleton(object):
    _instances = {}

    def __new__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(Singleton, cls).__new__(cls, *args, **kwargs)
        return cls._instances[cls]


class BaseClass(object):
    def __init__(self, data):
        self.value = random.random()
        self.data = data

    def asfaa(self):
        pass


class MyClass(BaseClass, Singleton):
    def __init__(self, data=3):
        super().__init__(data)
        self.a = random.random()

class MyClass1(BaseClass, Singleton):
    def __init__(self, data=3):
        super().__init__(data)
        self.a = random.random()


inst1 = MyClass(3)
inst2 = MyClass(5)

如果 def __init__(self, data=3)MyClass 不接受任何参数并且看起来像这样，那么一切都会正常工作：def __init__(self)
如果我__init__在上面的示例中提供参数，那么我会收到以下错误。

line 9, in __new__
cls._instances[cls] = super(Singleton, cls).__new__(cls, *args, **kwargs)
TypeError: object.__new__() takes exactly one argument (the type to instantiate)

您如何将参数传递给 MyClass 等？有什么问题？

在splash58的回答之后，我们设法得到了这个工作结果：

import random


class Singleton(object):
    _instances = {}

    def __new__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(Singleton, cls).__new__(cls)
        return cls._instances[cls]


class BaseClass(object):
    def __init__(self, data: int):
        self.value = random.random()
        self.data = data

    def asfaa(self):
        pass


class MyClass(BaseClass, Singleton):
    def __init__(self, data=0):
        if not hasattr(self, '_is_initialized'):
            super().__init__(data)
            self.a = random.random()
            self._is_initialized = True


class MyClass1(BaseClass, Singleton):
    def __init__(self, data=0):
        if not hasattr(self, '_is_initialized'):
            super().__init__(data)
            self.a = random.random()
            self._is_initialized = True


inst = MyClass(1)
print(inst, inst.a, inst.data)
inst1 = MyClass(1234)
print(inst1, inst1.a, inst1.data)

inst2 = MyClass1(123)
print(inst2, inst2.a, inst2.data)

执行结果：

<__main__.MyClass object at 0x7fd702199890> 0.40160478301994584 1
<__main__.MyClass object at 0x7fd702199890> 0.40160478301994584 1
<__main__.MyClass1 object at 0x7fd7021998d0> 0.6368002566047511 123
python