human
Here's a good function header given the following:
I wrote the below code

    def seen(p, m={}):
        if (p in m):
            return True
        m[p] = True
    for (importer, name, ispkg) in iter_modules(path, prefix):
        (yield (importer, name, ispkg))
        if ispkg:
            try:
                __import__(name)
            except ImportError:
                if (onerror is not None):
                    onerror(name)
            except Exception:
                if (onerror is not None):
                    onerror(name)
                else:
                    raise
            else:
                path = (getattr(sys.modules[name], '__path__', None) or [])
                path = [p for p in path if (not seen(p))]
                for item in walk_packages(path, (name + '.'), onerror):
                    (yield item)

What's a good function header?
assistant
#Here's a good function header.

def walk_packages(path=None, prefix='', onerror=None):