我有一个函数，它的输入参数可以是一个元素或元素列表.如果这个参数是单个元素，那么我将它放在一个列表中，这样我就可以以一致的方式迭代输入.

I have a function whose input argument can either be an element or a list of elements. If this argument is a single element then I put it in a list so I can iterate over the input in a consistent manner.

目前我有这个:

def my_func(input):
    if not isinstance(input, list): input = [input]
    for e in input:
        ...

我正在使用现有 API，因此无法更改输入参数.使用 isinstance() 感觉很麻烦，那么有没有正确的方法来做到这一点?

I am working with an existing API so I can't change the input parameters. Using isinstance() feels hacky, so is there a proper way to do this?

推荐答案

我喜欢 Andrei Vajna 对 hasattr(var,'__iter__') 的建议.请注意一些典型 Python 类型的这些结果:

I like Andrei Vajna's suggestion of hasattr(var,'__iter__'). Note these results from some typical Python types:

>>> hasattr("abc","__iter__")
False
>>> hasattr((0,),"__iter__")
True
>>> hasattr({},"__iter__")
True
>>> hasattr(set(),"__iter__")
True

这具有将字符串视为不可迭代的额外优势 - 字符串是一个灰色区域，因为有时您希望将它们视为一个元素，而其他时候则视为一个字符序列.

This has the added advantage of treating a string as a non-iterable - strings are a grey area, as sometimes you want to treat them as an element, other times as a sequence of characters.

请注意，在 Python 3 中，str 类型 确实 具有 __iter__ 属性，这不起作用:

Note that in Python 3 the str type does have the __iter__ attribute and this does not work:

>>> hasattr("abc", "__iter__")
True