class XMeta(type):

    def __new__(mcs, *args, **kwargs):
        """
        【第一步】
        元類用__new__創(chuàng)建類。只會(huì)調(diào)用一次

        __new__ 方法始終都是類的靜態(tài)方法凿歼，即使沒(méi)有被加上靜態(tài)方法裝飾器

        """
        print('[X-meta new]', mcs, args, kwargs)
        return type.__new__(mcs, *args, **kwargs)

    def __init__(cls, *args, **kwargs):
        """
        【第二步】
        元類創(chuàng)建類時(shí)調(diào)用該構(gòu)造方法缓醋，不需要返回值微驶。只會(huì)調(diào)用一次

        """

        print('[X-meta init]', cls, args, kwargs)
        super().__init__(*args, **kwargs)

    def __call__(cls, *args, **kwargs):
        """
        【第三步】
        類實(shí)例化時(shí)會(huì)調(diào)用幕侠。每次都會(huì)調(diào)用

        該方法里會(huì)依次調(diào)用類的 __new__, __init__

        """
        print('[X-meta call]', cls, args, kwargs)
        return super().__call__(*args, **kwargs)


class A(metaclass=XMeta):

    def __new__(cls, *args, **kwargs):
        """
        __new__ 方法始終都是類的靜態(tài)方法唤殴，即使沒(méi)有被加上靜態(tài)方法裝飾器
        __new__ 必須要有返回值

        ５祷尽Ｊ嗬铩０罅瘛Ｄ慕巍！翔怎！注意：
        return super().__new__(cls, *args, **kwargs)
        報(bào)錯(cuò)：
            TypeError: object.__new__() takes exactly one argument (the type to instantiate)
        解決：
            執(zhí)行 object.__ new__ 或 super().__new__ 時(shí)窃诉，只能傳cls參數(shù)，否則會(huì)報(bào)錯(cuò)

        參考：
            https://blog.csdn.net/LaoYuanPython/article/details/93642448
            https://blog.csdn.net/weixin_30954607/article/details/95152484
            https://ask.csdn.net/questions/1061620
        """

        print('[A new]', cls, args, kwargs)
        # return object.__new__(cls)  # 執(zhí)行父類（不是元類３嗵住Ｆ础）的創(chuàng)建方法
        return super().__new__(cls)

    def __init__(self, *args, **kwargs):
        """
        構(gòu)造方法，不需要返回值
        """
        print('[A init]', self, args, kwargs)

    def __call__(self, args, kwargs):
        """
        該方法使類的實(shí)例對(duì)象成為一個(gè)可調(diào)用對(duì)象
        """
        print('[A call]', self, args, kwargs)

    def echo(self, s='yes'):
        print('[A echo]', self, s)


a = A()


# 輸出
[X-meta new] <class '__main__.XMeta'> ('A', (), {'__module__': '__main__', '__qualname__': 'A', '__new__': <function A.__new__ at 0x10ad16b90>, '__init__': <function A.__init__ at 0x10ad16c20>, '__call__': <function A.__call__ at 0x10ad16cb0>, 'echo': <function A.echo at 0x10ad16d40>, '__classcell__': <cell at 0x10ad2a650: empty>}) {}
[X-meta init] <class '__main__.A'> ('A', (), {'__module__': '__main__', '__qualname__': 'A', '__new__': <function A.__new__ at 0x10ad16b90>, '__init__': <function A.__init__ at 0x10ad16c20>, '__call__': <function A.__call__ at 0x10ad16cb0>, 'echo': <function A.echo at 0x10ad16d40>, '__classcell__': <cell at 0x10ad2a650: XMeta object at 0x7fc485717050>}) {}
[X-meta call] <class '__main__.A'> () {}
[A new] <class '__main__.A'> () {}
[A init] <__main__.A object at 0x10ad2a850> () {}