René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Minor improvement to errors with (no) missing colon","articleBody":"Some invalid `for` statements currently give the specific error `expected ':'` even if there is a colon on the line. I think it would be a slight improvement to raise a more general error in these cases. This is how `while` and `if` already behave.\r\n\r\n**Current behaviour:**\r\n```python\r\n   \u003e\u003e\u003e for x in range(10)\r\n   ...   pass\r\n   Traceback (most recent call last):\r\n   SyntaxError: expected ':'\r\n\r\n   \u003e\u003e\u003e for x in range 10:\r\n   ...   pass\r\n   Traceback (most recent call last):\r\n   SyntaxError: expected ':'\r\n\r\n   \u003e\u003e\u003e for x in range 10\r\n   ...   pass\r\n   Traceback (most recent call last):\r\n   SyntaxError: expected ':'\r\n```\r\n**Proposed behaviour:**\r\n```python\r\n   \u003e\u003e\u003e for x in range(10)\r\n   ...   pass\r\n   Traceback (most recent call last):\r\n   SyntaxError: expected ':'\r\n\r\n   \u003e\u003e\u003e for x in range 10:\r\n   ...   pass\r\n   Traceback (most recent call last):\r\n   SyntaxError: invalid syntax\r\n\r\n   \u003e\u003e\u003e for x in range 10\r\n   ...   pass\r\n   Traceback (most recent call last):\r\n   SyntaxError: invalid syntax\r\n```\r\n\r\n**Proposed Implementation:**\r\nWould do it the same way `while` and `if` do it. For the for loop example it would be something like this:\r\n```diff\r\n--- a/Grammar/python.gram\r\n+++ b/Grammar/python.gram\r\n@@ -379,7 +379,7 @@ while_stmt[stmt_ty]:\r\n\r\n for_stmt[stmt_ty]:\r\n     | invalid_for_stmt\r\n-    | 'for' t=star_targets 'in' ~ ex=star_expressions \u0026\u0026':' tc=[TYPE_COMMENT] b=block el=[else_block] {\r\n+    | 'for' t=star_targets 'in' ~ ex=star_expressions ':' tc=[TYPE_COMMENT] b=block el=[else_block] {\r\n         _PyAST_For(t, ex, b, el, NEW_TYPE_COMMENT(p, tc), EXTRA) }\r\n     | ASYNC 'for' t=star_targets 'in' ~ ex=star_expressions \u0026\u0026':' tc=[TYPE_COMMENT] b=block el=[else_block] {\r\n         CHECK_VERSION(stmt_ty, 5, \"Async for loops are\", _PyAST_AsyncFor(t, ex, b, el, NEW_TYPE_COMMENT(p, tc), EXTRA)) }\r\n@@ -1295,6 +1295,7 @@ invalid_while_stmt:\r\n     | a='while' named_expression ':' NEWLINE !INDENT {\r\n         RAISE_INDENTATION_ERROR(\"expected an indented block after 'while' statement on line %d\", a-\u003elineno) }\r\n invalid_for_stmt:\r\n+    | 'for' star_targets 'in' star_expressions NEWLINE { RAISE_SYNTAX_ERROR(\"expected ':'\") }\r\n     | [ASYNC] a='for' star_targets 'in' star_expressions ':' NEWLINE !INDENT {\r\n         RAISE_INDENTATION_ERROR(\"expected an indented block after 'for' statement on line %d\", a-\u003elineno) }\r\n invalid_def_raw:\r\n```\r\nI'd also apply this to other suites where it makes sense (e.g. `with`, `match/case`, and `try`)\r\n\r\nWould it be OK for me to submit a PR making these changes? (this is my first time looking into the CPython parser so apologies if I made any obvious mistakes!)\r\n\r\n","author":{"url":"https://github.com/wookie184","@type":"Person","name":"wookie184"},"datePublished":"2022-05-16T19:38:35.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/92858/cpython/issues/92858"}