Because tests may have been updated or changed since this solution was approved, or because solutions were written with an older version of the language. Sometimes old solutions get invalidated but not always.

How is it possible to post a solution that doesn't pass the tests? Short code purdie though

It should be "...else x-2 * y...". or "for c in roman.reverse()"

@c4po
consider to read reduce documentation here https://docs.python.org/3/library/functools.html
"The left argument, x, is the accumulated value and the right argument, y, is the update value from the iterable"

someone hacked the main frame!

Wrong solution. Ex: MCM is 1900, wheras this solution returns 2100.

After playing around, I find that this doesn't actually seem to work. Could anyone tell me why tho? I can't find what is wrong with the code. Thanks.

Because people don't actually know how to read code or check to see if actually works. They think it is "clever" just because it is on one line.

❤️

Why is this wrong solution so highly upvoted?

you can check by "MCMXC"

Agreed. Interprets 'XIV' (14) as 16....

I second that! Agreed that it doesn't handle that edge case well.

I love this solution (in theory)! Unfortunately there's a bug in it - it incorrectly interprets XIX as 21, whereas it should be 19.

So sad though - love the approach.