处理单个元素或序列的通用函数

Question

我想要一个通用函数 get_me() 能够同时处理序列和单个元素参数。

代码如下：

from typing import Sequence

class class_1:
    def __init__(self, i: int=0):
        self.name = 'A'+str(i)

    def __repr__(self):
        return self.name

class class_2:
    def __init__(self, i: int=0):
        self.name = 'B'+str(i)

    def __repr__(self):
        return self.name

def get_me(seq: Sequence):

    for s in seq:
        print(f"\n1 is {s[0].name}, 2 is {s[1].name}")

这适用于以下所有组合：

one = class_1(1), class_2(1)
two = class_1(2), class_2(2)
three = class_1(3), class_2(3)

many = [one, two, three]
many = (one, two, three)
many = {one, two}
many = one, two

get_me(many)

...但给了TypeError

get_me(一个)

如果没有try: except，是否可以让这段代码处理它？

Answer 1

也许这就是你所追求的：

from typing import Sequence, Union, Tuple

# ...

def get_me(seq: Union[Sequence, Tuple]):
    if isinstance(seq, tuple):
        seq = (seq,)
    for s in seq:
        print(f"\n1 is {s[0].name}, 2 is {s[1].name}")

这依赖于单个元素是一个元组，就像在您的示例中一样 - 但您的 print 语句也是如此，所以这似乎是合理的。如果您需要它适用于任何类型，您可以将其替换为 Any 并检查它是否不是序列 - 但当然您还必须修改 print 语句以及使用的任何其他代码参数。

您注意到当您将many 定义为时，此解决方案不起作用：

many = one, two

没错，因为这也产生了很多Tuple。

为了支持这一点，你需要类似的东西：

def get_me(seq: Sequence):
    if not isinstance(seq[0], tuple):
        seq = (seq,)
    for s in seq:
        print(f"\n1 is {s[0].name}, 2 is {s[1].name}")

但是，这并不严格或明确。另一种方法是：

class SuperClass:
    pass


class Class1(SuperClass):
    # ...


class Class2(SuperClass):
    # ...


# ... 


def get_me(seq: Union[Sequence[SuperClass], SuperClass]):
    if isinstance(seq, SuperClass):
        seq = (seq,)
    for s in seq:
        print(f"\n1 is {s[0].name}, 2 is {s[1].name}")

如果所有显式输入都是必需的，我更喜欢哪种解决方案。

Answer 2

由于参数类型的各种可能排列，看起来try: except 无法避免，同时保持代码简单。

所以代码...

def get_me(seq: Sequence):

    try:
        for s in seq:
            print(f"\n1 is {s[0].name}, 2 is {s[1].name}")
    except (TypeError, AttributeError):
        print(f"\n1 is {seq[0].name}, 2 is {seq[1].name}")

...适用于我所有可能的情况：

one = class_1(1), class_2(1)
two = class_1(2), class_2(2)
three = class_1(3), class_2(3)

many = [one, two, three]
many = (one, two, three)
many = {one, two}
many = one, two

get_me(many)
get_me(one)
get_me(two)
get_me(three)