def register(function, first_interval: float=0, persistent: bool=False):
    """Add a new function that will be called after the specified amount of seconds. The function gets no arguments and is expected to return either None or a float. If None is returned, the timer will be unregistered. A returned number specifies the delay until the function is called again. functools.partial can be used to assign some parameters. 

    :param function: The function that should called. 
    :param first_interval: Seconds until the callback should be called the first time. 
    :type first_interval: float
    :param persistent: Don’t remove timer when a new file is loaded. 
    :type persistent: bool
    """
    pass
