In case it is helpful, here's my list of examples where the AC and existing signature objects are insufficiently expressive:


type(obj)
type(name, bases, mapping)
    two different signatures depending on type   

range(stop)
range(start, stop)
range(start, stop, step)

dict.pop(key[, default])
   default of None has different meaning than missing default
   which raises KeyError when the key is missing

itertools.permutations(iterable[, r])
   where the absence of *r* implies r=len(iterable)

bisect.bisect_right(a, x[, lo[, hi]]) -> index
   where the absence of *hi* implies hi=len(a)

min(iterable, *[, default=obj, key=func]) -> value
min(arg1, arg2, *args, *[, key=func]) -> value
   has two signatures depending on the number of
   positional arguments and a keyword argument
   only used in the first signature.  It's implementation
   is also shared with max().


dict() -> new empty dictionary
dict(mapping) -> new dictionary initialized from a mapping object's
   (key, value) pairs
dict(iterable) -> new dictionary initialized as if via:
   d = {}
   for k, v in iterable:
       d[k] = v
dict(**kwargs) -> new dictionary initialized with the name=value pairs
   in the keyword argument list.  For example:  dict(one=1, two=2)

def sumseq(seq, a=0, b=None):
    # Pure python code with nullable int
    if b is None:
        b = len(seq)
    return sum(seq[a:b])