Support Python 3.14 unparenthesized exception lists

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ## (0.41.0) UNRELEASED
 ### Added
+- Support Python 3.14 unparenthesized exception lists in `except` and `except*`
+  clauses (PEP 758).
 - New `DISABLE_SPLIT_LIST_WITH_COMMENT` flag.
  `DISABLE_SPLIT_LIST_WITH_COMMENT` is a new knob that changes the
   behavior of splitting a list when a comment is present inside the list.

third_party/yapf_third_party/_ylib2to3/Grammar.txt

@@ -119,7 +119,8 @@ try_stmt: ('try' ':' suite
 with_stmt: 'with' asexpr_test (',' asexpr_test)*  ':' suite
 
 # NB compile.c makes sure that the default except clause is last
-except_clause: 'except' ['*'] [test [(',' | 'as') test]]
+# PEP 758 allows an unparenthesized exception list without an 'as' target.
+except_clause: 'except' ['*'] [test ('as' test | (',' test)* [','])]
 suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT
 
 # Backward compatibility cruft to support:

yapf/yapflib/logical_line.py

@@ -297,8 +297,8 @@ def _SpaceRequiredBetween(left, right, is_line_disabled):
     # Spaces between keyword, string, number, and identifier tokens.
     return True
   if lval == ',' and rval == ':':
-    # We do want a space between a comma and colon.
-    return True
+    # Keep a space in slices, but not after a trailing exception-list comma.
+    return pytree_utils.NodeName(left.node.parent) != 'except_clause'
   if style.Get('SPACE_INSIDE_BRACKETS'):
     # Supersede the "no space before a colon or comma" check.
     if left.OpensScope() and rval == ':':

yapftests/pytree_utils_test.py

@@ -72,6 +72,15 @@ def testClassNotLocal(self):
     with self.assertRaises(SyntaxError):
       pytree_utils.ParseCodeToTree('class nonlocal: pass\n')
 
+  def testUnparenthesizedExceptClausesWithAs(self):
+    for keyword in ('except', 'except*'):
+      for exceptions in ('ValueError, TypeError', 'ValueError,'):
+        with self.subTest(keyword=keyword, exceptions=exceptions):
+          code = 'try:\n  pass\n{} {} as error:\n  pass\n'.format(
+              keyword, exceptions)
+          with self.assertRaises(SyntaxError):
+            pytree_utils.ParseCodeToTree(code)
+
 
 class InsertNodesBeforeAfterTest(yapf_test_helper.YAPFTest):
 

yapftests/reformatter_python3_test.py

@@ -19,6 +19,7 @@
 
 from yapf.yapflib import reformatter
 from yapf.yapflib import style
+from yapf.yapflib import yapf_api
 
 from yapftests import yapf_test_helper
 
@@ -30,6 +31,53 @@ class TestsForPython3Code(yapf_test_helper.YAPFTest):
   def setUpClass(cls):  # pylint: disable=g-missing-super-call
     style.SetGlobalStyle(style.CreatePEP8Style())
 
+  def testUnparenthesizedExceptClauses(self):
+    # https://github.com/google/yapf/issues/1319
+    for keyword in ('except', 'except*'):
+      for exceptions, formatted_exceptions in (
+          ('ZeroDivisionError,ValueError,IndexError',
+           'ZeroDivisionError, ValueError, IndexError'),
+          ('ValueError,TypeError,IndexError,KeyError',
+           'ValueError, TypeError, IndexError, KeyError'),
+          ('ValueError,', 'ValueError,'),
+          ('ValueError,TypeError,', 'ValueError, TypeError,'),
+      ):
+        with self.subTest(keyword=keyword, exceptions=exceptions):
+          unformatted_code = ('try:\n  x=1/0\n{} {}:\n  pass\n'.format(
+              keyword, exceptions))
+          expected_formatted_code = (
+              'try:\n    x = 1 / 0\n{} {}:\n    pass\n'.format(
+                  keyword.replace('*', ' *'), formatted_exceptions))
+          formatted_code, changed = yapf_api.FormatCode(
+              unformatted_code, style_config='pep8')
+          self.assertTrue(changed)
+          self.assertCodeEqual(expected_formatted_code, formatted_code)
+          self.assertEqual(
+              (formatted_code, False),
+              yapf_api.FormatCode(formatted_code, style_config='pep8'))
+
+  def testLongUnparenthesizedExceptClauses(self):
+    # Without parentheses, splitting the exception list would be invalid.
+    for keyword in ('except', 'except *'):
+      with self.subTest(keyword=keyword):
+        code = ('try:\n    pass\n'
+                '{} module.FirstException, module.SecondException, '
+                'module.ThirdException, module.FourthException:\n'
+                '    pass\n').format(keyword)
+        self.assertEqual((code, False),
+                         yapf_api.FormatCode(code, style_config='pep8'))
+
+  def testExistingExceptClauses(self):
+    for keyword in ('except', 'except *'):
+      for exceptions in ('ValueError', 'ValueError as error',
+                         '(ValueError, TypeError)',
+                         '(ValueError, TypeError) as error'):
+        with self.subTest(keyword=keyword, exceptions=exceptions):
+          code = 'try:\n    pass\n{} {}:\n    pass\n'.format(
+              keyword, exceptions)
+          self.assertEqual((code, False),
+                           yapf_api.FormatCode(code, style_config='pep8'))
+
   def testTypedNames(self):
     unformatted_code = textwrap.dedent("""\
         def x(aaaaaaaaaaaaaaa:int,bbbbbbbbbbbbbbbb:str,ccccccccccccccc:dict,eeeeeeeeeeeeee:set={1, 2, 3})->bool: