Save to a file object works, but is not documented
Created originally on Bitbucket by walkerjim
For various reasons I'd like to open my own file-like object and pass it as the destination to a workbook's save method.
Tracing through the code and actually trying it out, I find that this works, at least in my chosen case.
I suggest that the interface specification be changed so that this is explicitly supported. Of course, you'd probably have to check through other places in the code to make sure this doesn't break anything, but I figure you'd be able to recognize that a whole lot faster than I would.