Renumbered again so that the messaging OO style comes immediately after the hash OO style

14-bulletin-board/README.md

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+Style #13
+==============================
+
+Constraints:
+
+- Larger problem is decomposed into entities using some form of abstraction
+  (objects, modules or similar)
+
+- The entities are never called on directly for actions
+
+- Existence of an infrastructure for publishing and subscribing to
+  events, aka the bulletin board
+
+- Entities post event subscriptions (aka 'wanted') to the bulletin
+  board and publish events (aka 'offered') to the bulletin board. the
+  bulletin board does all the event management and distribution
+
+Possible names:
+
+- Bulletin board
+- Publish-Subscribe

14-bulletin-board/tf-14.py

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+#!/usr/bin/env python
+import sys, re, operator, string
+
+#
+# The event management substrate
+#
+class EventManager:
+    def __init__(self):
+        self._subscriptions = {}
+
+    def subscribe(self, event_type, handler):
+        if event_type in self._subscriptions:
+            self._subscriptions[event_type].append(handler)
+        else:
+            self._subscriptions[event_type] = [handler]
+
+    def publish(self, event):
+        event_type = event[0]
+        if event_type in self._subscriptions:
+            for h in self._subscriptions[event_type]:
+                h(event)
+
+#
+# The application entities
+#
+class DataStorage:
+    """ Models the contents of the file """
+    def __init__(self, event_manager):
+        self._event_manager = event_manager
+        self._event_manager.subscribe('load', self.load)
+        self._event_manager.subscribe('start', self.produce_words)
+
+    def load(self, event):
+        path_to_file = event[1]
+        with open(path_to_file) as f:
+            self._data = f.read()
+        pattern = re.compile('[\W_]+')
+        self._data = pattern.sub(' ', self._data).lower()
+
+    def produce_words(self, event):
+        data_str = ''.join(self._data)
+        for w in data_str.split():
+            self._event_manager.publish(('word', w))
+        self._event_manager.publish(('eof', None))
+
+class StopWordFilter:
+    """ Models the stop word filter """
+    def __init__(self, event_manager):
+        self._stop_words = []
+        self._event_manager = event_manager
+        self._event_manager.subscribe('load', self.load)
+        self._event_manager.subscribe('word', self.is_stop_word)
+
+    def load(self, event):
+        with open('../stop_words.txt') as f:
+            self._stop_words = f.read().split(',')
+        self._stop_words.extend(list(string.ascii_lowercase))
+
+    def is_stop_word(self, event):
+        word = event[1]
+        if word not in self._stop_words:
+            self._event_manager.publish(('valid_word', word))
+
+class WordFrequencyCounter:
+    """ Keeps the word frequency data """
+    def __init__(self, event_manager):
+        self._word_freqs = {}
+        self._event_manager = event_manager
+        self._event_manager.subscribe('valid_word', self.increment_count)
+        self._event_manager.subscribe('print', self.print_freqs)
+
+    def increment_count(self, event):
+        word = event[1]
+        if word in self._word_freqs:
+            self._word_freqs[word] += 1
+        else:
+            self._word_freqs[word] = 1
+
+    def print_freqs(self, event):
+        word_freqs = sorted(self._word_freqs.iteritems(), key=operator.itemgetter(1), reverse=True)
+        for (w, c) in word_freqs[0:25]:
+            print w, ' - ', c
+
+class WordFrequencyApplication:
+    def __init__(self, event_manager):
+        self._event_manager = event_manager
+        self._event_manager.subscribe('run', self.run)
+        self._event_manager.subscribe('eof', self.stop)
+
+    def run(self, event):
+        path_to_file = event[1]
+        self._event_manager.publish(('load', path_to_file))
+        self._event_manager.publish(('start', None))
+
+    def stop(self, event):
+        self._event_manager.publish(('print', None))
+
+#
+# The main function
+#
+em = EventManager()
+DataStorage(em), StopWordFilter(em), WordFrequencyCounter(em)
+WordFrequencyApplication(em)
+em.publish(('run', sys.argv[1]))