====== Pure python and very simple event management library ======

In event driven programming events are crucial. My requirements was [[http://micropython.org/|Micropython]] platform on ESP32 micro-controller, so i could not use any other events library out-there. I've stumbled one very basic, very simple library and gave it a try... and it worked out-of-the-box for my case. When testing various event management libs out there I've stumbled on something similar, but it did not worked within classes. Python is nothing but classes everywhere :)

I was testing and extended this very simple python script, that perfectly works as main element in event driven development.

Strengths of library: 
  * Observer can be declared before event type is created
  * Events can be fired even if there is no observers.
  * Works as pure python script
  * Works on micropython platform
  * Event name can be any string

I'm using this solution for event for timer, that fires each second and observe "ticker" where i need to update clock. I use clock in multiple places in my micropython script and i can get away with just one hardware timer used.

Honorable mentions goes to Pithikos from StackOverflow [[https://stackoverflow.com/a/28479007|this answer]]

I have extended this library with possibility to forget event.

<code python EventObserver.py>
class Observer():
    _observers = []

    def __init__(self):
        self._observers.append(self)
        self._observed_events = []

    def observe(self, event_name, callback_fn):
        self._observed_events.append({'event_name': event_name, 'callback_fn': callback_fn})

    def forget(self, event_name):
        for dict_item in self._observed_events:
            for key, val in dict_item.items():
                if val == event_name:
                    self._observed_events.remove(dict_item)


class Event():
    def __init__(self, event_name, *callback_args):
        for observer in Observer._observers:
            for observable in observer._observed_events:
                if observable['event_name'] == event_name:
                    observable['callback_fn'](*callback_args)


</code>
Here is example of how to use this library
<code python example.py>
import EventObserver

# class object MUST inherit Observer object if you use it within class
class Room(Observer):
    def __init__(self):
        print("Room is ready.")
        Observer.__init__(self)  # DON'T FORGET THIS
        # observer can be declared already in class init method with following line
        # this.observe('someone sneezed', this.someone_sneezed)

    def someone_arrived(self, who):
        print("{} has arrived!".format(who))
        
    def someone_sneezed(self, who):
        print("{} has just sneezed!".format(who))


# Observe for specific event
room = Room()
room.observe('arrived', room.someone_arrived)
room.observe('sneezed', room.someone_arrived)

# Fire some events
Event('left', 'John')       # no events are attached to event "someone left" 
Event('arrived', 'Lenard')  # will output "Lenard has arrived!"
Event('sneezed', 'Jenny')   # will output "Jenny has just sneezed!"

# Remove known event
room.forget('arrived')

# no events based on 'someone arrived' will be fired
'''
</code>


{{tag> event driven programming python micropython events library tutorial }}

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