Modernize code to Python 3.6+ and some cleanup

03-dict-set/index_default.py

@@ -16,7 +16,7 @@ with open(sys.argv[1], encoding='utf-8') as fp:
     for line_no, line in enumerate(fp, 1):
         for match in WORD_RE.finditer(line):
             word = match.group()
-            column_no = match.start()+1
+            column_no = match.start() + 1
             location = (line_no, column_no)
             index[word].append(location)  # <2>