Produce the list of annotations for a given key.

def get_annotations(event, key, namespace=None, matchfunc=None):
    """Produce the list of annotations for a given key."""
    if matchfunc is None:
        matchfunc = _is_equal
    if isinstance(key, Exception):
        key = _error_repr(key)
    return [ann for ann in event.get("_humilis", {}).get("annotation", [])
            if (matchfunc(key, ann["key"]) and
                (namespace is None or ann.get("namespace") == namespace))]