bpo-33224: PEP 479 fix for difflib.mdiff() (GH-6381) (GH-6390)

Author: miss-islington

Lib/difflib.py

@@ -1634,14 +1634,18 @@ def _line_pair_iterator():
  lines_to_write -= 1
  # Now yield the context lines after the change
  lines_to_write = context-1
- while(lines_to_write):
- from_line, to_line, found_diff = next(line_pair_iterator)
- # If another change within the context, extend the context
- if found_diff:
- lines_to_write = context-1
- else:
- lines_to_write -= 1
- yield from_line, to_line, found_diff
+ try:
+ while(lines_to_write):
+ from_line, to_line, found_diff = next(line_pair_iterator)
+ # If another change within the context, extend the context
+ if found_diff:
+ lines_to_write = context-1
+ else:
+ lines_to_write -= 1
+ yield from_line, to_line, found_diff
+ except StopIteration:
+ # Catch exception from next() and return normally
+ return
 
 
 _file_template = """

Lib/test/test_difflib.py

@@ -93,6 +93,14 @@ def test_added_tab_hint(self):
  self.assertEqual("+ \t\tI am a bug", diff[2])
  self.assertEqual("? +\n", diff[3])
 
+ def test_mdiff_catch_stop_iteration(self):
+ # Issue #33224
+ self.assertEqual(
+ list(difflib._mdiff(["2"], ["3"], 1)),
+ [((1, '\x00-2\x01'), (1, '\x00+3\x01'), True)],
+ )
+
+
 patch914575_from1 = """
  1. Beautiful is beTTer than ugly.
  2. Explicit is better than implicit.

Misc/NEWS.d/next/Library/2018-04-04-23-41-30.bpo-33224.pyR0jB.rst

@@ -0,0 +1,2 @@
+Update difflib.mdiff() for PEP 479. Convert an uncaught StopIteration in a
+generator into a return-statement.