Why does pyyaml disallow trailing spaces in block scalars?

We do not permit trailing spaces for block scalars.

Block style (|, <) is overruled with quoted style (") if the string contains trailing spaces. I don’t see any reason for this, and the fact that I can’t force a certain style (even it means losing information) has caused me a lot of grief.

[oulenz]

Thank you @perlpunk for these examples, they perfectly illustrate what I mean, and thank you both for looking into this.

My use case was that I had a large number of dictionaries that I wanted to store as yaml records, in | block style. Some of these happened to have trailing spaces and were output wrongly, as a double quoted scalar. This was frustrating because

1. I had to reverse-engineer why this was happening, especially since I couldn’t find any reason in the yaml spec why my strings shouldn’t be representable in | block style. This really boggles the mind: pyyaml is needlessly deviating from the yaml spec. So this is a bug, that should be fixed.
2. I was explicitly telling the emitter that I wanted | block style. The way every other Python function that I know of works is that the option I set is obeyed, possibly leading to warnings and/or errors, and that the consequences (like losing information in edge cases) are for me to deal with. This is programming, I should be able to control things. For pyyaml to override my option due to style considerations really is not acceptable.

My ‘solution’ was to strip trailing spaces before emitting so I would get | block style across the board, so ironically, this led me to lose information I wouldn’t have lost otherwise.

[perlpunk]

@ingydotnet , I was trying to give examples, to every reader of this issue, where I can understand the wish for block style to be preserved. I was not writing this to imply that you don’t know how it works.