gh-116325: Raise SyntaxError rather than IndexError on ForwardRef with empty string arg (#116341)

sobolevn · web-flow · commit a29998a06bf7 · 2024-03-05T09:14:18.000Z
diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
@@ -5867,6 +5867,12 @@ def foo(a: 'Node[T'):
         with self.assertRaises(SyntaxError):
             get_type_hints(foo)
 
+    def test_syntax_error_empty_string(self):
+        for form in [typing.List, typing.Set, typing.Type, typing.Deque]:
+            with self.subTest(form=form):
+                with self.assertRaises(SyntaxError):
+                    form['']
+
     def test_name_error(self):
 
         def foo(a: 'Noode[T]'):
diff --git a/Lib/typing.py b/Lib/typing.py
@@ -880,7 +880,7 @@ def __init__(self, arg, is_argument=True, module=None, *, is_class=False):
         # If we do `def f(*args: *Ts)`, then we'll have `arg = '*Ts'`.
         # Unfortunately, this isn't a valid expression on its own, so we
         # do the unpacking manually.
-        if arg[0] == '*':
+        if arg.startswith('*'):
             arg_to_compile = f'({arg},)[0]'  # E.g. (*Ts,)[0] or (*tuple[int, int],)[0]
         else:
             arg_to_compile = arg
diff --git a/Misc/NEWS.d/next/Library/2024-03-05-02-09-18.gh-issue-116325.FmlBYv.rst b/Misc/NEWS.d/next/Library/2024-03-05-02-09-18.gh-issue-116325.FmlBYv.rst
@@ -0,0 +1,2 @@
+:mod:`typing`: raise :exc:`SyntaxError` instead of :exc:`AttributeError`
+on forward references as empty strings.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+:mod:`typing`: raise :exc:`SyntaxError` instead of :exc:`AttributeError`
	`2`	`+on forward references as empty strings.`