Filter an annotation by only leaving the parameters of type "ptype".

def filter_annotations_by_ptype(function, ptype):
    '''Filter an annotation by only leaving the parameters of type "ptype".'''
    ret = {}
    for k, v in function.__annotations__.items():
        if k == 'return':
            continue
        pt, _ = v
        if pt == ptype:
            ret[k] = v
    return ret