类型（名称、基础、字典）是否可用于创建实例（类的对象），例如在 Singleton 中

Question

所以有object.__new__(cls)和super().__new__(cls)函数可以用来创建实例，但是我可以用type(name, bases, dict)(*args, **kwargs)来创建实例吗？

class Singleton(object):

  instance = None

  def __init__(self, *args, **kwargs):
    pass

  def __new__(cls, *args, **kwargs):
    if isinstance(cls.instance, type(None)):
      mcls = cls.__class__
      cls.instance = type(mcls.__name__, mcls.__bases__, dict(cls.__dict__))(*args, *kwargs)

    return cls.instance

s = Singleton()
print(s)

Answer 1

所以我找不到将__new__ 方法保留在cls.__dict__ 中的方法，它会导致递归，所以我在创建类之前将其删除。

class FooMixin(object):
  def print_somth(self):
    print('smth....')


class Singleton(FooMixin):

  instance = None

  def __new__(cls, *args, **kwargs):
    if cls.instance is None:
      temp = dict(cls.__dict__)
      del temp['__new__']
      temp['test'] = 100
      cls.instance = type('Singleton', cls.__bases__, temp)(*args, **kwargs)
    return cls.instance

s = Singleton()
print(s.test, s.print_somth())