Added style #19. True story.

19-defensive/README.md

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+Style #19
+==============================
+
+Constraints:
+
+- Every single procedure and function checks the sanity of its
+  arguments and either returns something sensible when the arguments
+  are unreasonable or assigns them reasonable values
+
+- All code blocks check for all possible errors and escape the block
+  when things go wrong
+
+Possible names:
+
+- Defensive
+- Pessimistic
+- Never trust the caller nor the callee

19-defensive/tf-19.py

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+#!/usr/bin/env python
+
+import sys, re, operator, string, inspect
+
+#
+# The functions
+#
+def extract_words(path_to_file):
+    """
+    Takes a path to a file and returns the non-stop
+    words, after properly removing nonalphanumeric chars
+    and normalizing for lower case
+    """
+    if type(path_to_file) is not str or not path_to_file:
+        return []
+
+    try:
+        with open(path_to_file) as f:
+            str_data = f.read()
+    except IOError as e:
+        print "I/O error({0}) when opening {1}: {2}".format(e.errno, path_to_file, e.strerror)
+        return []
+    
+    pattern = re.compile('[\W_]+')
+    word_list = pattern.sub(' ', str_data).lower().split()
+
+    try:
+        with open('../stop_words.txt') as f:
+            stop_words = f.read().split(',')
+    except IOError as e:
+        print "I/O error({0}) when opening ../stops_words.txt: {1}".format(e.errno, e.strerror)
+        return []
+
+    stop_words.extend(list(string.ascii_lowercase))
+    return [w for w in word_list if not w in stop_words]
+
+def frequencies(word_list):
+    """
+    Takes a list of words and returns a dictionary associating
+    words with frequencies of occurrence
+    """
+    if type(word_list) is not list or word_list == []:
+        return {}
+
+    word_freqs = {}
+    for w in word_list:
+        if w in word_freqs:
+            word_freqs[w] += 1
+        else:
+            word_freqs[w] = 1
+    return word_freqs
+
+def sort(word_freq):
+    """
+    Takes a dictionary of words and their frequencies
+    and returns a list of pairs where the entries are
+    sorted by frequency 
+    """
+    if type(word_freq) is not dict or word_freq == {}:
+        return []
+
+    return sorted(word_freq.iteritems(), key=operator.itemgetter(1), reverse=True)
+
+#
+# The main function
+#
+word_freqs = sort(frequencies(extract_words(sys.argv[1])))
+
+for tf in word_freqs[0:25]:
+    print tf[0], ' - ', tf[1]
+