Improve syntax error for non-case statement inside match statement

Author: brianschubert

Grammar/python.gram

@@ -1503,6 +1503,7 @@ invalid_case_block:
     | "case" patterns guard? NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }
     | a="case" patterns guard? ':' NEWLINE !INDENT {
         RAISE_INDENTATION_ERROR("expected an indented block after 'case' statement on line %d", a->lineno) }
+    | !"case" { RAISE_SYNTAX_ERROR_ON_NEXT_TOKEN("expected 'case' statement inside 'match' statement") }
 invalid_as_pattern:
     | or_pattern 'as' a="_" { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "cannot use '_' as a target") }
     | or_pattern 'as' a=expression {

Lib/test/test_syntax.py

@@ -356,7 +356,7 @@
 >>> match x:
 ...     y = 3
 Traceback (most recent call last):
-SyntaxError: invalid syntax
+SyntaxError: expected 'case' statement inside 'match' statement
 
 >>> match x:
 ...     case y:
@@ -3466,6 +3466,38 @@ def test_match_stmt_invalid_as_expr(self):
             end_offset=15 + len("obj.attr"),
         )
 
+    def test_match_stmt_contains_invalid_stmt(self):
+        for stmt in [
+            "a",
+            "a = 1",
+            "if a:",
+            "else:",
+            "match 1:"
+            "pass",
+            "return",
+            "return 2",
+            "raise Exception('a')",
+            "del a",
+            "yield 2",
+            "assert False",
+            "break",
+            "continue",
+            "import",
+            "import ast",
+            "from",
+            "from ast import *"
+        ]:
+            self._check_error(
+                textwrap.dedent(
+                    f"""
+                    match 1:
+                        {stmt}
+                    """
+                ),
+                errtext="expected 'case' statement inside 'match' statement",
+                lineno=3,
+            )
+
     def test_ifexp_else_stmt(self):
         msg = "expected expression after 'else', but statement is given"
 

Misc/NEWS.d/next/Core_and_Builtins/2026-03-28-14-09-16.gh-issue-146582.wlpY3D.rst

@@ -0,0 +1,3 @@
+Improve :exc:`SyntaxError` message when a statement other than a
+:keyword:`case` statement appears inside a :keyword:`match` statement.
+Patch by Brian Schubert.