The curly bracket separator is assigned to “curl”, but then the previous “curly” variable is tested:

https://hg.python.org/cpython/annotate/3.5/Tools/clinic/clinic.py#l202

name, curl, trailing = trailing.partition('}')
if not curly or name not in kwargs:
    ...

I presume the fix is to assign to “curly”, but I haven’t had a chance to figure out how to test it yet.