Singleton在Cython不工作 [英] Singleton is not working in Cython

问题描述

这是我定义Singleton的方式。

This is how i define Singleton.

class Singleton(type):
    _instances = {}
    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
        return cls._instances[cls]

然后我定义了我的课程如：

Then I have my classes defined as:

class MyClass(object):
    __metaclass__ = Singleton

    def __init__(self):
        pass


a = MyClass()
b = MyClass()

a is b将返回True

"a is b" will return True

但是

cdef class MyCythonClass(object):
    __metaclass__ = Singleton

    def __cinit__(self):
        pass

c = MyCythonClass()
d = MyCythonClass()

c is d将返回False

"c is d" will return False

我认为这是正在运行的c代码（cinit）前init，所以我试图将cinit放回init，它也不起作用。
如果我在类之前删除了 cdef，问题就解决了。

I thought it is the c code (cinit) running before init and so I tried to put the cinit back to init, it doesnt work either. The problem is solved if i removed the "cdef" before "class"

我想知道为什么，可能我在这里错过了一些重要的东西。

I am wondering why, probably I am missing something important here. Your help would be much appreciated.

Win 10 / Python 2.7

Win 10 / Python 2.7

推荐答案

Cython似乎不支持现成的元类。但是此模块可能提供了一种解决方法。

Cython does not appear to support meta classes out of the box. But this module may provide a workaround.

如下所示实施单例可能是另一种（更安全的）选择：

Implementing the singleton as follows may be another (safer) alternative:

cdef class Singleton:
    _instances = {}

    @classmethod
    def instance(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = cls(*args, **kwargs)
        return cls._instances[cls]

cdef class MyCythonClass(Singleton):
    pass

c = MyCythonClass.instance()
d = MyCythonClass.instance()
c is d  # True

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