added video tut for chain of responsibility, started on observer pattern

Author: Sean-Bradley

chain_of_responsibility/README.md

@@ -7,7 +7,7 @@ The objects in the chain will decide how to process them and/or pas them to the
 The objects can also modify the next in the chain if for example you wanted to run objects in a recursive manner.
 
 
-## Chain of Responsibility UML Diagram
+## Chain of Responsibility Diagram
 ![Chain of Responsibility UML Diagram](chain_of_responsibility.png)
 
 
@@ -43,4 +43,8 @@ Dispensing 2 £50 note
 Dispensing 1 £20 note
 Dispensing 1 £10 note
 Go spoil yourself
-```
+```
+
+## Chain of Responsibility Video Tutorial
+[![Chain of Responsibility Video Tutorial](https://img.youtube.com/vi/1z1Z79cOtCE/0.jpg)](https://youtu.be/1z1Z79cOtCE)
+

observer/classes.dot

@@ -0,0 +1,17 @@
+digraph "classes" {
+charset="utf-8"
+rankdir=BT
+"0" [label="{ABCWeather|\l|update()\l}", shape="record"];
+"1" [label="{BBCWeather|\l|update()\l}", shape="record"];
+"2" [label="{COLD|name\lvalue\l|}", shape="record"];
+"3" [label="{IObserver|\l|update()\l}", shape="record"];
+"4" [label="{NBCWeather|\l|update()\l}", shape="record"];
+"5" [label="{RAINY|name\lvalue\l|}", shape="record"];
+"6" [label="{SUNNY|name\lvalue\l|}", shape="record"];
+"7" [label="{WINDY|name\lvalue\l|}", shape="record"];
+"8" [label="{Weather|\l|notify()\lregister()\lremove_observer()\l}", shape="record"];
+"9" [label="{WeatherType|\l|}", shape="record"];
+"0" -> "3" [arrowhead="empty", arrowtail="none"];
+"1" -> "3" [arrowhead="empty", arrowtail="none"];
+"4" -> "3" [arrowhead="empty", arrowtail="none"];
+}

observer/observer.py

@@ -0,0 +1,78 @@
+from abc import ABCMeta, abstractstaticmethod
+from enum import Enum
+import time
+
+
+class WeatherType(Enum):
+    SUNNY = 1
+    RAINY = 2
+    WINDY = 3
+    COLD = 4
+
+
+class Weather():
+    """Observable"""
+
+    def __init__(self):
+        self._observers = set()
+        pass
+
+    def register(self, observer):
+        self._observers.add(observer)
+
+    def remove_observer(self, observer):
+        self._observers.remove(observer)
+
+    def notify(self, weather_type):
+        for observer in self._observers:
+            observer.update(weather_type)
+
+
+class IObserver(metaclass=ABCMeta):
+
+    @abstractstaticmethod
+    def update(WeatherType):
+        """Update all the registered observers"""
+
+
+class BBCWeather(IObserver):
+    def __init__(self, observable):
+        observable.register(self)
+
+    def update(self, weather_type):
+        print(f"{__class__} : {repr(weather_type)}")
+
+
+class ABCWeather(IObserver):
+    def __init__(self, observable):
+        observable.register(self)
+
+    def update(self, weather_type):
+        print(f"{__class__} : {repr(weather_type)}")
+
+
+class NBCWeather(IObserver):
+    def __init__(self, observable):
+        observable.register(self)
+
+    def update(self, weather_type):
+        print(f"{__class__} : {repr(weather_type)}")
+
+
+if __name__ == "__main__":
+
+    WEATHERSERVICE = Weather()
+
+    BBCWEATHER = BBCWeather(WEATHERSERVICE)
+    ABCWEATHER = ABCWeather(WEATHERSERVICE)
+    NBCWEATHER = NBCWeather(WEATHERSERVICE)
+
+    WEATHERSERVICE.notify(WeatherType.RAINY)
+    WEATHERSERVICE.remove_observer(BBCWEATHER)
+    time.sleep(2)
+    WEATHERSERVICE.notify(WeatherType.SUNNY)
+    WEATHERSERVICE.remove_observer(NBCWEATHER)
+    time.sleep(2)
+    WEATHERSERVICE.notify(WeatherType.WINDY)
+    time.sleep(2)
+    WEATHERSERVICE.notify(WeatherType.COLD)