Python:将标量视为一个元素列表 [英] python: treating a scalar as a one element list

问题描述

我正在编写一个处理从文件读取的列表的python脚本:

I am writing a python script that process lists read from a file:

l = readListFromFile( myFile )
for i in l :
    # do something to each element

当l具有多个元素时，一切正常.
但是，当列表中只有一个元素时，readFromFile返回l作为标量而不是列表.因此for i in l失败并显示错误

All works fine when l has more than one element.
However, when there is only one element in the list readFromFile returns l as a scalar and not as a list. Hence for i in l fails with error

对象不可迭代

object is not iterable

我无法控制readFromFile ，我的问题是，即使l仅具有单个元素，我如何使python将l视为列表? /p>

I have no control over readFromFile, and my question is how can I make python treat l as a alist even in the case where l has only a single element?

推荐答案

一个简单的解决方案是

l = readListFromFile(myFile)
try:
    i = iter(l)
    if isinstance(l, str):
        i = l 
except TypeError:
    i = [l]
for .... in i

即使您更改了readListFromFile以返回另一个可迭代对象，这也将起作用.

This will work even if you change what readListFromFile to return another iterable.

如果可以保证是一个str或一个列表(或其他可迭代的)，那么一个衬板解决方案就是

A one liner solution if it's guaranteed to be a str or a list (or other iterable) is just

l = readListFromFile(myFile)
for e in [l] if isinstance(l, str) else l:

仅使用三元运算符.

顺便说一句，拥有一个名为readList的方法...并不总是返回列表就是邪恶的.

On an aside, having a method called readList... not always returning a list is just evil.

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