gh-129922: Promote _mdiff to a public function

Doc/library/difflib.rst

@@ -338,6 +338,26 @@ Diff generation
       + tree
       + emu
 
+.. function:: mdiff(fromlines, tolines, context=None, linejunk=None, charjunk=IS_CHARACTER_JUNK)
+
+   Return a generator yielding marked up *fromlines* and *tolines* side by side differences.
+
+   Optional keyword parameters *context* is number of lines to display on each side the difference, if ``None``, all from/to text lines will be generated; *linejunk* and *charjunk* are filtering functions.
+
+   from/to line tuple -- (line num, line text)
+      line num -- integer or None (to indicate a context separation)
+      line text -- original line text with following markers inserted:
+
+         ``'\0+'`` -- marks start of added text
+
+         ``'\0-'`` -- marks start of deleted text
+
+         ``'\0^'`` -- marks start of changed text
+
+         ``'\1'`` -- marks end of added/deleted/changed text
+
+   boolean flag -- None indicates context separation, True indicates
+        either "from" or "to" line contains a change, otherwise False.
 
 .. function:: restore(sequence, which)
 

Lib/difflib.py

@@ -10,6 +10,9 @@
 Function ndiff(a, b):
     Return a delta: the difference between `a` and `b` (lists of strings).
 
+Function mdiff(fromlines, tolines):
+    Return a generator yielding marked up from/to side by side differences.
+
 Function restore(delta, which):
     Return one of the two sequences that generated an ndiff delta.
 
@@ -26,7 +29,7 @@
     For producing HTML side by side comparison with change highlights.
 """
 
-__all__ = ['get_close_matches', 'ndiff', 'restore', 'SequenceMatcher',
+__all__ = ['get_close_matches', 'ndiff', 'mdiff', 'restore', 'SequenceMatcher',
            'Differ','IS_CHARACTER_JUNK', 'IS_LINE_JUNK', 'context_diff',
            'unified_diff', 'diff_bytes', 'HtmlDiff', 'Match']
 
@@ -1358,7 +1361,7 @@ def ndiff(a, b, linejunk=None, charjunk=IS_CHARACTER_JUNK):
     """
     return Differ(linejunk, charjunk).compare(a, b)
 
-def _mdiff(fromlines, tolines, context=None, linejunk=None,
+def mdiff(fromlines, tolines, context=None, linejunk=None,
            charjunk=IS_CHARACTER_JUNK):
     r"""Returns generator yielding marked up from/to side by side differences.
 
@@ -2025,7 +2028,7 @@ def make_table(self,fromlines,tolines,fromdesc='',todesc='',context=False,
             context_lines = numlines
         else:
             context_lines = None
-        diffs = _mdiff(fromlines,tolines,context_lines,linejunk=self._linejunk,
+        diffs = mdiff(fromlines,tolines,context_lines,linejunk=self._linejunk,
                       charjunk=self._charjunk)
 
         # set up iterator to wrap lines that exceed desired width

Lib/test/test_difflib.py

@@ -114,7 +114,7 @@ def test_hint_indented_properly_with_tabs(self):
     def test_mdiff_catch_stop_iteration(self):
         # Issue #33224
         self.assertEqual(
-            list(difflib._mdiff(["2"], ["3"], 1)),
+            list(difflib.mdiff(["2"], ["3"], 1)),
             [((1, '\x00-2\x01'), (1, '\x00+3\x01'), True)],
         )
 

Misc/NEWS.d/next/Library/2026-09-02-23-38-40.gh-issue-129922.Klr4dt.rst

@@ -0,0 +1 @@
+Promote ``difflib._mdiff()`` to a public function named :func:`difflib.mdiff`.