Optional characters in Save Template for Adding Books

[Starson17]

My original books are all in a standard name format of:
format 1:
Lastname, Firstname - Series ## - Title.ext

Of course, some books have no Series, and they are in this format:
format 2:
Lastname, Firstname - Title.ext

I have a regex in the Adding Books Preferences page that always splits the name correctly, regardless of which of the two forms are drag/dropped into Calibre. The regex relies on the space-hyphen-space to do the splitting.

I'd like to be able to export from Calibre with Save Books in a way that would reproduce the same name that the book had when it was imported. That's pretty easy if all books were in one form, but the problem arises when a book does not have a series. If I use the series and series_number in the Save Template, I need to separate it by the space-hyphen-space, but if there's no series, that space-hyphen-space separator always appears in the filename. The result is that I get an extra space-hyphen-space in the filename when there's no series.

My question: Is there any way to make the space-hyphen-space separator optionally dependent on the presence or absence of the series so that the output name is in format 1 when there is a series, and in format 2 when there isn't? Is there some trick to this that I've missed? Thanks!

[kovidgoyal]

the templates use pythons format strings, as far as I recall there's no way to do conditionals in those.