Replacement

Consider the following configuration snippet in addition to the configuration of the mqtt service shown above:

def lookup_data(data):
    if type(data) == dict and 'fruit' in data:
            return "Ananas"
    return None

Then, in the section defining the topic we listen on:

...
[test/topic]
#format =  Since when does a {fruit} cost {price}?
format =  lookup_data()

We've replaced the formatmap entry for the topic by a function which you define within the functions file you configure as functions in mqttwarn.ini configuration file. These functions are invoked with decoded JSON data passed to them as a dict. The string returned by the function returned string replaces the outgoing message:

in/a1 {"fruit":"pineapple", "price": 131, "tst" : "1391779336"}
out/food Ananas
out/fruit/pineapple Ananas

If a function operating on a message (i.e. within format =) returns None or an empty string, the target notification is suppressed.