Python自定义对象实现切片功能的介绍（代码示例）

class MyList():
    def __init__(self):
        self.data = []
    def append(self, item):
        self.data.append(item)
    def __getitem__(self, key):
        print("key is : " + str(key))
        return self.data[key]

l = MyList()
l.append("My")
l.append("name")
l.append("is")
l.append("Python猫")

print(l[3])
print(l[:2])
print(l['hi'])

### 输出结果：
key is : 3
Python猫
key is : slice(None, 2, None)
['My', 'name']
key is : hi
Traceback (most recent call last):
...
TypeError: list indices must be integers or slices, not str

###略去其它代码####
def __getitem__(self, index):
    cls = type(self)
    if isinstance(index, slice):  # 如果index是个切片类型，则构造新实例
       return cls(self._components[index])
    elif isinstance(index, numbers.Integral):  # 如果index是个数，则直接返回
        return self._components[index]
    else:
        msg = "{cls.__name__} indices must be integers"
        raise TypeError(msg.format(cls=cls))

class MyDict():
    def __init__(self):
        self.data = {}
    def __len__(self):
        return len(self.data)
    def append(self, item):
        self.data[len(self)] = item
    def __getitem__(self, key):
        if isinstance(key, int):
            return self.data[key]
        if isinstance(key, slice):
            slicedkeys = list(self.data.keys())[key]
            return {k: self.data[k] for k in slicedkeys}
        else:
            raise TypeError

d = MyDict()
d.append("My")
d.append("name")
d.append("is")
d.append("Python猫")
print(d[2])
print(d[:2])
print(d[-4:-2])
print(d['hi'])

### 输出结果：
is
{0: 'My', 1: 'name'}
{0: 'My', 1: 'name'}
Traceback (most recent call last):
...
TypeError