evennia/docs/source/Howtos/Tutorial-Weather-Effects.md

# Adding Weather messages to a Room


This tutorial will have us create a simple weather system for our MUD.  The way we want to use this is to have all outdoor rooms echo weather-related messages to the room at regular and semi-random intervals. Things like "Clouds gather above", "It starts to rain" and so on.

One could imagine every outdoor room in the game having a script running on themselves that fires regularly. For this particular example it is however more efficient to do it another way, namely by using a "ticker-subscription" model. 

The principle is simple: Instead of having each Object individually track the time, they instead subscribe to be called by a global ticker who handles time keeping.  Not only does this centralize and organize much of the code in one place, it also has less computing overhead.

Evennia's [TickerHandler](../Components/TickerHandler.md) specifically offers such a subscription model. We will use it for our weather system.

We will create a new WeatherRoom typeclass that is aware of the day-night cycle.

```{code-block} python
:linenos:
:emphasize-lines: 

    import random
    from evennia import DefaultRoom, TICKER_HANDLER
    
    ECHOES = ["The sky is clear.", 
              "Clouds gather overhead.",
              "It's starting to drizzle.",
              "A breeze of wind is felt.",
              "The wind is picking up"] # etc  

    class WeatherRoom(DefaultRoom):
        "This room is ticked at regular intervals"        
       
        def at_object_creation(self):
            "called only when the object is first created"
            TICKER_HANDLER.add(60 * 60, self.at_weather_update)

        def at_weather_update(self, *args, **kwargs):
            "ticked at regular intervals"
            echo = random.choice(ECHOES)
            self.msg_contents(echo)
```



In the `at_object_creation` method, we simply added ourselves to the TickerHandler and tell it to
call `at_weather_update` every hour (`60*60` seconds). During testing you might want to play with a
shorter time duration.

For this to work we also create a custom hook `at_weather_update(*args, **kwargs)`, which is the
call sign required by TickerHandler hooks.

Henceforth the room will inform everyone inside it when the weather changes. This particular example
is of course very simplistic - the weather echoes are just randomly chosen and don't care what
weather came before it. Expanding it to be more realistic is a useful exercise.