Cleanup and modernize code prior to working on Issue 11747.

Lib/difflib.py

@@ -1188,22 +1188,23 @@ def unified_diff(a, b, fromfile='', tofile='', fromfiledate='',
     started = False
     for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
         if not started:
-            fromdate = '\t%s' % fromfiledate if fromfiledate else ''
-            todate = '\t%s' % tofiledate if tofiledate else ''
-            yield '--- %s%s%s' % (fromfile, fromdate, lineterm)
-            yield '+++ %s%s%s' % (tofile, todate, lineterm)
             started = True
-        i1, i2, j1, j2 = group[0][1], group[-1][2], group[0][3], group[-1][4]
-        yield "@@ -%d,%d +%d,%d @@%s" % (i1+1, i2-i1, j1+1, j2-j1, lineterm)
+            fromdate = '\t{}'.format(fromfiledate) if fromfiledate else ''
+            todate = '\t{}'.format(tofiledate) if tofiledate else ''
+            yield '--- {}{}{}'.format(fromfile, fromdate, lineterm)
+            yield '+++ {}{}{}'.format(tofile, todate, lineterm)
+        first, last = group[0], group[-1]
+        i1, i2, j1, j2 = first[1], last[2], first[3], last[4]
+        yield '@@ -{},{} +{},{} @@{}'.format(i1+1, i2-i1, j1+1, j2-j1, lineterm)
         for tag, i1, i2, j1, j2 in group:
             if tag == 'equal':
                 for line in a[i1:i2]:
                     yield ' ' + line
                 continue
-            if tag == 'replace' or tag == 'delete':
+            if tag in {'replace', 'delete'}:
                 for line in a[i1:i2]:
                     yield '-' + line
-            if tag == 'replace' or tag == 'insert':
+            if tag in {'replace', 'insert'}:
                 for line in b[j1:j2]:
                     yield '+' + line
 
@@ -1252,38 +1253,38 @@ def context_diff(a, b, fromfile='', tofile='',
       four
     """
 
+    prefix = dict(insert='+ ', delete='- ', replace='! ', equal='  ')
     started = False
-    prefixmap = {'insert':'+ ', 'delete':'- ', 'replace':'! ', 'equal':'  '}
     for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
         if not started:
-            fromdate = '\t%s' % fromfiledate if fromfiledate else ''
-            todate = '\t%s' % tofiledate if tofiledate else ''
-            yield '*** %s%s%s' % (fromfile, fromdate, lineterm)
-            yield '--- %s%s%s' % (tofile, todate, lineterm)
             started = True
+            fromdate = '\t{}'.format(fromfiledate) if fromfiledate else ''
+            todate = '\t{}'.format(tofiledate) if tofiledate else ''
+            yield '*** {}{}{}'.format(fromfile, fromdate, lineterm)
+            yield '--- {}{}{}'.format(tofile, todate, lineterm)
 
-        yield '***************%s' % (lineterm,)
-        if group[-1][2] - group[0][1] >= 2:
-            yield '*** %d,%d ****%s' % (group[0][1]+1, group[-1][2], lineterm)
+        first, last = group[0], group[-1]
+        yield '***************{}'.format(lineterm)
+
+        if last[2] - first[1] > 1:
+            yield '*** {},{} ****{}'.format(first[1]+1, last[2], lineterm)
         else:
-            yield '*** %d ****%s' % (group[-1][2], lineterm)
-        visiblechanges = [e for e in group if e[0] in ('replace', 'delete')]
-        if visiblechanges:
+            yield '*** {} ****{}'.format(last[2], lineterm)
+        if any(tag in {'replace', 'delete'} for tag, _, _, _, _ in group):
             for tag, i1, i2, _, _ in group:
                 if tag != 'insert':
                     for line in a[i1:i2]:
-                        yield prefixmap[tag] + line
+                        yield prefix[tag] + line
 
-        if group[-1][4] - group[0][3] >= 2:
-            yield '--- %d,%d ----%s' % (group[0][3]+1, group[-1][4], lineterm)
+        if last[4] - first[3] > 1:
+            yield '--- {},{} ----{}'.format(first[3]+1, last[4], lineterm)
         else:
-            yield '--- %d ----%s' % (group[-1][4], lineterm)
-        visiblechanges = [e for e in group if e[0] in ('replace', 'insert')]
-        if visiblechanges:
+            yield '--- {} ----{}'.format(last[4], lineterm)
+        if any(tag in {'replace', 'insert'} for tag, _, _, _, _ in group):
             for tag, _, _, j1, j2 in group:
                 if tag != 'delete':
                     for line in b[j1:j2]:
-                        yield prefixmap[tag] + line
+                        yield prefix[tag] + line
 
 def ndiff(a, b, linejunk=None, charjunk=IS_CHARACTER_JUNK):
     r"""