Python idiom for taking the single item from a list

Excellent. That one belongs in any Python style guide. Though technically it's not a style, it does lead to better readability, and reduces the propensity for unforseen consequences.

As a commenter there noted,

[thing] = stuff

works too. I think I like that even better.

So we have

so if I was wrong in my original assumption that stuff has exactly one element, Python will shout at me before this will manifest itself as a hard-to-find bug someplace else in the program.

and then later on,

This method works even when stuff is a set or any other kind of collection. stuff[0] wouldn’t work on a set because set doesn’t support access by index number.

The second argument is basically in favor of duck-typing which is the pythonic way of writing code, ie, not caring about the actual object but only if it responds to the given message.

But what about the first argument? Couldn't you make the case that the pythonic way of handling it is to only care about if the object responds to __getitem__(0)?

Which idiom you use would depend entirely on context, wouldn't it?

My problem is that exact situation almost never comes up. Usually, I want to use the item in the list directly in an expression, not assign it to another variable first. For example:

    if 1==len(lst):
        return lst[0]
    else:
        return reduce(fn, lst)

I don't really want to have to do:

    if 1==len(lst):
        (single,)=lst
        return single
    else:
        return reduce(fn, lst)

I think this style has one great drawback: it requires deeper knowledge of Python then the 'usual' thing = stuff[0].