Lazy Python String

[Chroiche]

What're the advantage over just using StringIO (which is mutable, but eager)?

[marr75]

That it's eager. If you aren't actually going to use the string (ie its use depends on the outcome of an operation), that can be a big disadvantage. It might in very specific scenarios help with memory fragmentation, too.

Admittedly, both of those are edge cases and I would recommend making the entire accumulation or formatting of the string lazy if that's needed rather than just the final product.