I don't remember, do we absolutely need to check the length?

What about lookup_revisions?

you could use map or a generator here.

In general, personally, i avoid round-trips if i can avoid it.

You could also use map

map(converters.from_revisions, revisions)

or a generator ^^

(converters.from_revision(x) for x in revisions)

The superior layer does the translation before serializing anyway.

Impact: You'll need to force the lazyness in your tests for this function (by wrapping your call in a list for example).

children path

if not prev_sha1s:

you can remove the else: altogether.

I feel it's too easy to misread lookup_revisions as lookup_revision or the other way around.

This creates a problem with backend call args checking, which I'm currently solving.

That's a good point ^^