python类实例的某些属性是唯一的

我会用一个元类。此解决方案避免调用 __init__() 太多次了:

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

class MyClass(metaclass=CachedInstance):
    def __init__(self, name):
        self.name = name

a = MyClass('Instance 1');
b = MyClass('Instance 2');
c = MyClass('Instance 1');
assert a is c
assert a is not b

参考及详细说明: https://stackoverflow.com/a/6798042/8747

这是可以做到的(假设 args 都是散列的)

 class MyClass:

     instances = {}

     def __new__(cls, *args):
          if args in cls.instances:
               return cls.instances[args]
          self = super().__new__(cls)
          cls.instances[args] = self
          return self

a = MyClass('hello')
b = MyClass('hello')
c = MyClass('world')

a is b and a == b and a is not c and a != c  # True

is 是显示两个对象是同一实例的python运算符。 == 回到 是 在没有被遮住的物体上。

正如评论中指出的,如果您有 __init__ 有副作用。下面是一个避免这种情况的实现:

class Coord:

     num_unique_instances = 0
     _instances = {}

     def __new__(cls, x, y):

         if (x, y) in cls._instances:
              return cls._instances[x, y]

         self = super().__new__(cls)

         # __init__ logic goes here  -- will only run once
         self.x = x
         self.y = y
         cls.num_unique_instances += 1
         # __init__ logic ends here

         cls._instances[x, y] = self
         return self

     # no __init__ method