Check that the default is in the list, and not empty

def _check_default_index(items, default_index):
    '''Check that the default is in the list, and not empty'''
    num_items = len(items)
    if default_index is not None and not isinstance(default_index, int):
        raise TypeError("The default index ({}) is not an integer".format(default_index))
    if default_index is not None and default_index >= num_items:
        raise ValueError("The default index ({}) >= length of the list ({})".format(default_index, num_items))
    if default_index is not None and default_index < 0:
        raise ValueError("The default index ({}) < 0.".format(default_index))
    if default_index is not None and not items[default_index]:
        raise ValueError("The default index ({}) points to an empty item.".format(default_index))