diff --git a/21-the-flow/README.md b/21-the-flow/README.md
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+Style #21
+==============================
+
+Constraints:
+
+- No returns before the end of procedures or functions
+
+- No breaks or continues in iterations
+
+Possible names:
+
+- The flow
+
+
diff --git a/21-the-flow/tf-21.py b/21-the-flow/tf-21.py
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+++ b/21-the-flow/tf-21.py
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+#!/usr/bin/env python
+
+import sys, re, operator, string, inspect
+
+# Reusing the defensive style program to illustrate this
+
+#
+# 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
+    """
+    fail = False
+    word_list = []
+    if type(path_to_file) is str and path_to_file:
+        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)
+            fail = True
+    
+        if not fail:
+            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)
+                fail = True
+
+            if not fail:
+                stop_words.extend(list(string.ascii_lowercase))
+
+    return [w for w in word_list if not w in stop_words] if not fail else []
+
+def frequencies(word_list):
+    """
+    Takes a list of words and returns a dictionary associating
+    words with frequencies of occurrence
+    """
+    if type(word_list) is list and word_list <> []:
+        word_freqs = {}
+        for w in word_list:
+            if w in word_freqs:
+                word_freqs[w] += 1
+            else:
+                word_freqs[w] = 1
+        return word_freqs
+    else:
+        return {}
+
+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 dict and word_freq <> {}:
+        return sorted(word_freq.iteritems(), key=operator.itemgetter(1), reverse=True)
+    else:
+        return []
+
+#
+# The main function
+#
+filename = sys.argv[1] if len(sys.argv) > 1 else "../input.txt"
+word_freqs = sort(frequencies(extract_words(filename)))
+
+for tf in word_freqs[0:25]:
+    print tf[0], ' - ', tf[1]
+