Prints the specified message as a warning; prepends "WARNING" to
    the message, so that can be left off.

def warn(msg, level=0, prefix=True):
    """Prints the specified message as a warning; prepends "WARNING" to
    the message, so that can be left off.
    """
    if will_print(level):
        printer(("WARNING: " if prefix else "") + msg, "yellow")