def _pad_post_array(input_array, length):
    """
    Pads the input 2D list with 0's at the end so that is is of shape (None, length)
    :param input_array: 2D list
    :param length: length to pad to
    :return: (None, length) padded array
    """
    output_array = []
    for arr in input_array:
        padded = arr + (length - len(arr))*[0]
        output_array.append(padded)
    return output_array