Update of rotate_pairs

code/rotate_pairs.py

@@ -1,11 +1,8 @@
 """This module contains a code example related to
-
 Think Python, 2nd Edition
 by Allen Downey
 http://thinkpython2.com
-
 Copyright 2015 Allen Downey
-
 License: http://creativecommons.org/licenses/by/4.0/
 """
 
@@ -14,32 +11,41 @@
 from rotate import rotate_word
 
 
-def make_word_dict():
-    """Read the words in words.txt and return a dictionary
-    that contains the words as keys"""
-    d = dict()
-    fin = open('words.txt')
-    for line in fin:
-        word = line.strip().lower()
-        d[word] = None
+def make_word_list():
+    """Read the words in words.txt and return a list
+    that contains the words."""
+    with open('words.txt') as fin:
+        word_list = []
+        for line in fin:
+            word = line.strip().lower()
+            word_list.append(word)
+
+    return word_list
 
-    return d
 
-
-def rotate_pairs(word, word_dict):
-    """Prints all words that can be generated by rotating word.
-
-    word: string
-    word_dict: dictionary with words as keys
+def rotate_pairs(word_list):
+    """Return list of all rotate pairs found in word_list.
+    word_list: list of words
     """
-    for i in range(1, 14):
-        rotated = rotate_word(word, i)
-        if rotated in word_dict:
-            print(word, i, rotated)
+    rotate_pairs = {}
+
+    for word in word_list:
+        first_letter = word[0]
+        if first_letter.isupper():
+            ref_letter = ord('A')
+        elif first_letter.islower():
+            ref_letter = ord('a')
+
+        # Create a rotated word which always starts with "A" or "a"
+        # and use it as a key to store the word in the rotate_pairs dict.
+        rotated_word = rotate_word(word, ref_letter - ord(first_letter))
+        rotate_pairs.setdefault(rotated_word, []).append(word)
+
+    # Rotate pairs are contained in the lists that have more than one word.
+    rotate_pairs = [item for item in rotate_pairs.values() if len(item) > 1]
+    return rotate_pairs
 
 
 if __name__ == '__main__':
-    word_dict = make_word_dict()
-
-    for word in word_dict:
-        rotate_pairs(word, word_dict)
+    word_list = make_word_list()
+    all_rotate_pairs = rotate_pairs(word_list)