Fix invalid rule for ifexp if statement given after else

- also reword error messages - move tests to test_syntax - update whatsnew and news
python · pablogsal · Feb 18, 2025 · Feb 9, 2025 · Feb 9, 2025 · Feb 9, 2025
commit 903d9b6515f7df3c1e0f62b38c8ac24f6690a1c0
@@ -174,26 +174,30 @@ Improved error messages
          ^^^^^^^
      ValueError: too many values to unpack (expected 3, got 4)
 
-* If a statement (:keyword:`!pass`, :keyword:`!del`, :keyword:`!return`, :keyword:`!yield`,
-  :keyword:`!raise`, :keyword:`!break`, :keyword:`!continue`, :keyword:`!assert`)
-  is passed to the :ref:`if_expr`, then the error message highlights where
-  the :token:`~python-grammar:expression` is required.
 
-  .. code-block:: pycon
+* If a statement (:keyword:`pass`, :keyword:`del`, :keyword:`return`,
+  :keyword:`yield`, :keyword:`raise`, :keyword:`break`, :keyword:`continue`,
+  :keyword:`assert`, :keyword:`import`, :keyword:`from`) is passed to the
+  :ref:`if_expr` after :keyword:`else`, or one of the :keyword:`pass`,
+  :keyword:`break`, :keyword:`continue` is passed before :keyword:`if`, then the
+  error message highlights where the :token:`~python-grammar:expression` is
+  required. (Contributed by Sergey Miryanov in :gh:`129515`.)
+
+  .. code-block:: python
 
      >>> x = 1 if True else pass
      Traceback (most recent call last):
        File "<string>", line 1
          x = 1 if True else pass
                             ^^^^
-     SyntaxError: statement given where 'orelse' expression required
+     SyntaxError: expected expression after 'else', but statement is given
 
      >>> x = continue if True else break
      Traceback (most recent call last):
        File "<string>", line 1
          x = continue if True else break
              ^^^^^^^^
-     SyntaxError: statement given where 'body' expression required
+     SyntaxError: expected expression before 'if', but statement is given
 
 
 * When incorrectly closed strings are detected, the error message suggests

@@ -1196,11 +1196,10 @@ invalid_expression:
         _PyPegen_check_legacy_stmt(p, a) ? NULL : p->tokens[p->mark-1]->level == 0 ? NULL :
         RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax. Perhaps you forgot a comma?") }
    | a=disjunction 'if' b=disjunction !('else'|':') { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "expected 'else' after 'if' expression") }
-   | a=disjunction 'if' b=disjunction 'else' c[stmt_ty]=(
-        return_stmt | raise_stmt | pass_stmt | del_stmt | yield_stmt | assert_stmt | break_stmt | continue_stmt) {
-        RAISE_SYNTAX_ERROR_KNOWN_LOCATION (c, "statement given where 'orelse' expression required") }
+   | a=disjunction 'if' b=disjunction 'else' !expression {
+        RAISE_SYNTAX_ERROR_ON_NEXT_TOKEN("expected expression after 'else', but statement is given") }
    | a[stmt_ty]=(pass_stmt|break_stmt|continue_stmt) 'if' b=disjunction 'else' c=simple_stmt {
-        RAISE_SYNTAX_ERROR_KNOWN_LOCATION (a, "statement given where 'body' expression required") }
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION (a, "expected expression before 'if', but statement is given") }
    | a='lambda' [lambda_params] b=':' &FSTRING_MIDDLE  {
         RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "f-string: lambda expressions are not allowed without parentheses") }
 

diff --git a/Lib/test/test_ast/test_ast.py b/Lib/test/test_ast/test_ast.py
@@ -1966,42 +1966,6 @@ def test_ifexp(self):
         for args in (s, l, l), (l, s, l), (l, l, s):
             self.expr(ast.IfExp(*args), "must have Load context")
 
-    def test_ifexp_orelse_stmt(self):
-        msg = "statement given where 'orelse' expression required"
-        for stmt in [
-            "x = 1 if 1 else pass",
-            "x = 1 if 1 else return",
-            "x = 1 if 1 else raise Exception('a')",
-            "x = 1 if 1 else del a",
-            "x = 1 if 1 else yield 2",
-            "x = 1 if 1 else assert False",
-            "x = 1 if 1 else break",
-            "x = 1 if 1 else continue"
-        ]:
-            with self.subTest(stmt), self.assertRaisesRegex(SyntaxError, msg):
-                ast.parse(stmt)
-
-    def test_ifexp_body_stmt_orelse_expression(self):
-        msg = "statement given where 'body' expression required"
-        for stmt in [
-            "x = pass if 1 else 1",
-            "x = break if 1 else 1",
-            "x = continue if 1 else 1"
-        ]:
-            with self.subTest(stmt), self.assertRaisesRegex(SyntaxError, msg):
-                ast.parse(stmt)
-
-    def test_ifexp_body_stmt_orelse_stmt(self):
-        msg = "statement given where 'body' expression required"
-        for stmt in [
-            "x = pass if 1 else pass",
-            "x = break if 1 else pass",
-            "x = continue if 1 else pass",
-            "x = continue if 1 else import ast"
-        ]:
-            with self.subTest(stmt), self.assertRaisesRegex(SyntaxError, msg):
-                ast.parse(stmt)
-
     def test_dict(self):
         d = ast.Dict([], [ast.Name("x", ast.Load())])
         self.expr(d, "same number of keys as values")

diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
@@ -2863,6 +2863,34 @@ def test_match_stmt_invalid_as_expr(self):
             end_offset=15 + len("obj.attr"),
         )
 
+    def test_ifexp_else_stmt(self):
+        msg = "expected expression after 'else', but statement is given"
+        self._check_error("x = 1 if 1 else pass", msg)
+        self._check_error("x = 1 if 1 else return", msg)
+        self._check_error("x = 1 if 1 else return 2", msg)
+        self._check_error("x = 1 if 1 else raise Exception('a')", msg)
+        self._check_error("x = 1 if 1 else del a", msg)
+        self._check_error("x = 1 if 1 else yield 2", msg)
+        self._check_error("x = 1 if 1 else assert False", msg)
+        self._check_error("x = 1 if 1 else break", msg)
+        self._check_error("x = 1 if 1 else continue", msg)
+        self._check_error("x = 1 if 1 else import", msg)
+        self._check_error("x = 1 if 1 else import ast", msg)
+        self._check_error("x = 1 if 1 else from", msg)
+        self._check_error("x = 1 if 1 else from ast import *", msg)
+
+    def test_ifexp_body_stmt_else_expression(self):
+        msg = "expected expression before 'if', but statement is given"
+        self._check_error("x = pass if 1 else 1", msg)
+        self._check_error("x = break if 1 else 1", msg)
+        self._check_error("x = continue if 1 else 1", msg)
+
+    def test_ifexp_body_stmt_else_stmt(self):
+        msg = "expected expression before 'if', but statement is given"
+        self._check_error("x = pass if 1 else pass", msg)
+        self._check_error("x = break if 1 else pass", msg)
+        self._check_error("x = continue if 1 else pass", msg)
+        self._check_error("x = continue if 1 else import ast", msg)
 
 def load_tests(loader, tests, pattern):
     tests.addTest(doctest.DocTestSuite())

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-02-09-11-30-38.gh-issue-129515.3L3vmo.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-02-09-11-30-38.gh-issue-129515.3L3vmo.rst
@@ -1,2 +1,2 @@
 Clarify syntax error messages for conditional expressions if statement
-specified in body and orelse parts.
+specified before ``if`` or after ``else`` keywords.