observer pattern

ramalho · ramalho · commit c5fff6ea0cdf · 2015-08-14T18:52:32.000-03:00
diff --git a/observer/README.md b/observer/README.md
@@ -0,0 +1,4 @@
+# Observer pattern
+
+Code example adapted from page 334 in chapter 14, *Useful Design Patterns* of the book [Expert Python Programming](https://www.packtpub.com/application-development/expert-python-programming) (Packt, 2008) by **Tarek Ziadé**.
+
diff --git a/observer/observer.py b/observer/observer.py
@@ -0,0 +1,55 @@
+"""
+    >>> WriteEvent.register(log)
+    >>> WriteEvent.notify('file #1')
+    file #1 was written
+    >>> WriteEvent.register(AnotherObserver())
+    >>> WriteEvent.notify('file #2')
+    file #2 was written
+    Yeah WriteEvent told me!
+
+"""
+
+
+class Event(object):
+    _observers = []
+
+    def __init__(self, subject):
+        self.subject = subject
+
+    @classmethod
+    def register(cls, observer):
+        if observer not in cls._observers:
+            cls._observers.append(observer)
+
+    @classmethod
+    def unregister(cls, observer):
+        if observer in cls._observers:
+            self._observers.remove(observer)
+
+    @classmethod
+    def notify(cls, subject):
+        event = cls(subject)
+        for observer in cls._observers:
+            observer(event)
+
+class WriteEvent(Event):
+
+    def __repr__(self):
+        return 'WriteEvent'
+
+def log(event):
+    print('%s was written' % event.subject)
+
+
+class AnotherObserver(object):
+    def __call__(self, event):
+        print('Yeah %s told me!' % event)
+
+if __name__ == '__main__':
+    import doctest
+    failed, attempted = doctest.testmod()
+    if not failed:
+        print('OK: %s tests passed' % attempted)
+    else:
+        print('FAIL: %s test(s) failed (of %s total)'
+              % (failed, attempted))

-Original file line number
+Diff line change
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 +# Observer pattern
++
 +Code example adapted from page 334 in chapter 14, *Useful Design Patterns* of the book [Expert Python Programming](https://www.packtpub.com/application-development/expert-python-programming) (Packt, 2008) by **Tarek Ziadé**.
++