def indent_code(input_string):
    """
    Split code by newline character, and prepend 4 spaces to each line.
    """
    lines = input_string.strip().split("\n")
    output_string = ""
    for line in lines:
        output_string += "    {}\n".format(line)
    ## one last newline for luck
    output_string += "\n"
    return output_string