[anamax]

I've used both, for with else more often. It avoided some booleans and if's that would have been much less clear/easy to get wrong.

I'd like a different name for for "for's" else.

I've been using method/function redefinition in place of conditionals related to initialization.

[greggyb]

Raymond Hettinger has a good section on this, tracing it back Knuth's discourse on structured programming in the face of 'goto'. He suggests calling the keyword 'nobreak', rather than 'else'.

Inside any loop are a conditional and a jump. In pseudocode:

    if not <loop end condition> then
        <do loop things>
        <jump to top of loop>
    else //loop is done
        <do things in the case that the loop has terminated naturally>

If we 'break' in the body of the loop for some reason, we will never hit the 'else' in this chunk of code. As Mr. Hettinger explains, this is obvious to anyone reading Knuth or coming from a 'goto' style of control flow. This is not an insult, but an observation. (Un)Fortunately, structured programming is the absolute norm now, and we learn looping constructs directly, rather than learning 'goto' and then building to looping constructs. Especially in a language with rich iteration protocols, such as Python, it is very much unapparent that the looping constructs are fancy wrappers around 'goto'.

Link to the talk: https://youtu.be/OSGv2VnC0go?t=948

[asicsp]

From Python docs (https://docs.python.org/3/tutorial/controlflow.html#break-an...):

>When used with a loop, the else clause has more in common with the else clause of a try statement than it does with that of if statements: a try statement’s else clause runs when no exception occurs, and a loop’s else clause runs when no break occurs.

[AlphaSite]

It’s consistent with try…else and if…else so I actually think it’s ok.

[63]

"else" usually means "instead of" or "otherwise" in those patterns. If the original case doesn't run, then the else case runs instead.

In a for loop, the else clause only runs if the loop successfully completes (isn't broken), so the else in for-else means the total opposite of what it means in every other pattern.

I think it would make a lot more sense if it were replaced with "done" or "upon" or something else that communicates how it works.

[housecarpenter]

It depends on whether you think of the break as success or failure. When I write a loop with a break it's usually some kind of search where the break happens once you've found something, and in that case the break is more of a success.

[jermy]

The way you describe is how it worked in zope templates (allowing a 'no items here' text if there was nothing to iterate over in a list) - it was frustrating that the later python implementation was different.

[ptx]

You could read it as "either process all of these elements, or otherwise do this other thing". If we break, we're not processing all of the elements (the normal case), so we do the "else" part instead.

Edit: This is wrong. See replies.

[63]

That would make total sense if it were correct. That's exactly how I think most people would intuit it

However, that's exactly how it doesn't work and that's my point. The else clause is only ran if the loop DOESN'T break.

[ptx]

Hmm! Yes, you're right. Even though I knew exactly how it works and I sometimes use it, I still got confused, so maybe it is a confusing feature after all. :)