Why python 3.6 requirement?

[zippeurfou]

I don't see any reason why this code would not run in a lower version of python.
Could you explain why is there such a requirement?

[Luolc]

Mainly because we only tested AdaBound on Python 3.6 and 3.7 and just leave it as-is before...

Yes, this is a really defensive setting and we are supposed to fix it. I believe no changes are needed for 3.5.
But I have no experience with 2.7. It seems that the format syntax is invalid in 2.7. Do you have any idea of making the code compatible with 2.7?