def gen_params(raw_params):
    u"""
    Generator that yields tuples of (name, default_value) for each parameter in the list
    If no default is given, then it is default_value is None (not Leaf(token.NAME, 'None'))
    """
    assert raw_params[0].type == token.STAR and len(raw_params) > 2
    curr_idx = 2  # the first place a keyword-only parameter name can be is index 2
    max_idx = len(raw_params)
    while curr_idx < max_idx:
        curr_item = raw_params[curr_idx]
        prev_item = curr_item.prev_sibling
        if curr_item.type != token.NAME:
            curr_idx += 1
            continue
        if prev_item is not None and prev_item.type == token.DOUBLESTAR:
            break
        name = curr_item.value
        nxt = curr_item.next_sibling
        if nxt is not None and nxt.type == token.EQUAL:
            default_value = nxt.next_sibling
            curr_idx += 2
        else:
            default_value = None
        yield (name, default_value)
        curr_idx += 1