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gh-151303 : Improve SyntaxError suggestions for common operator typos and cross-language mistakes #151375

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gh-151303 : Improve SyntaxError suggestions for common operator typos and cross-language mistakes #151375

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9472172
Improve SyntaxError suggestions for common operator typos
Aniketsy Jun 11, 2026
65cf172
add question mark in the suggestion and tests
Aniketsy Jun 12, 2026
34a7ef1
update tests
Aniketsy Jun 12, 2026
431174b
📜🤖 Added by blurb_it.
blurb-it[bot] Jun 12, 2026
bb79f1f
improve syntaxerror message <> typo
Aniketsy Jun 13, 2026
30e8188
Update Misc/NEWS.d/next/Core_and_Builtins/2026-06-12-03-41-39.gh-issu…
Aniketsy Jun 13, 2026
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9 changes: 9 additions & 0 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -801,8 +801,14 @@ compare_op_bitwise_or_pair[CmpopExprPair*]:
| in_bitwise_or
| isnot_bitwise_or
| is_bitwise_or
| invalid_diamond_op
| invalid_eqeqeq

invalid_diamond_op:
| a='<' b='>' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax. Maybe you meant '!=' instead of '<>'?") }

@StanFromIreland StanFromIreland Jun 13, 2026

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Won't this break when __future__.CO_FUTURE_BARRY_AS_BDFL is true?

@Aniketsy Aniketsy Jun 13, 2026

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hmm , yes

aniket@DESKTOP-074O80J:/mnt/d/cpython/cpython$ ./python.exe -c "
__futu> from __future__ import barry_as_FLUFL
> 1 < > 2
> "
  File "<string>", line 3
    1 < > 2
      ^^^
SyntaxError: invalid syntax.  Maybe you meant '!=' instead of '<>'?

please let me know your thoughts on this ...

aniket@DESKTOP-074O80J:/mnt/d/cpython/cpython$ git diff Grammar/python.gram
diff --git a/Grammar/python.gram b/Grammar/python.gram
index 61a6d5ea90..19ef406437 100644
--- a/Grammar/python.gram
+++ b/Grammar/python.gram
@@ -805,7 +805,11 @@ compare_op_bitwise_or_pair[CmpopExprPair*]:
     | invalid_eqeqeq

 invalid_diamond_op:
-    | a='<' b='>' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '!=' instead of '<>'?") }
+    | a='<' b='>' {
+        (p->flags & PyPARSE_BARRY_AS_BDFL)
+        ? RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '<>' instead of '< >'?")
+        : RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '!=' instead of '<>'?")
+    }
 eq_bitwise_or[CmpopExprPair*]: '==' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Eq, a) }
 invalid_eqeqeq:
     | a='==' b='=' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '==' instead of '==='?") }

output:

aniket@DESKTOP-074O80J:/mnt/d/cpython/cpython$ ./python.exe -c "1 < > 2"
  File "<string>", line 1
    1 < > 2
      ^^^
SyntaxError: invalid syntax.  Maybe you meant '!=' instead of '<>'?

aniket@DESKTOP-074O80J:/mnt/d/cpython/cpython$ ./python.exe -c "
__futu> from __future__ import barry_as_FLUFL
> 1 < > 2
> "
  File "<string>", line 3
    1 < > 2
      ^^^
SyntaxError: invalid syntax.  Maybe you meant '<>' instead of '< >'?

eq_bitwise_or[CmpopExprPair*]: '==' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Eq, a) }
invalid_eqeqeq:
| a='==' b='=' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax. Maybe you meant '==' instead of '==='?") }
noteq_bitwise_or[CmpopExprPair*]:
| (tok='!=' { _PyPegen_check_barry_as_flufl(p, tok) ? NULL : tok}) a=bitwise_or {_PyPegen_cmpop_expr_pair(p, NotEq, a) }
lte_bitwise_or[CmpopExprPair*]: '<=' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, LtE, a) }
Expand Down Expand Up @@ -1313,6 +1319,9 @@ invalid_assignment:
"'%s' is an illegal expression for augmented assignment",
_PyPegen_get_expr_name(a)
)}
| star_expressions a='=' b='<' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax. Maybe you meant '<=' instead of '=<'?") }
| star_expressions a='=' b='>' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax. Maybe you meant '>=' instead of '=>'?") }
| star_expressions a='=' b='!' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax. Maybe you meant '!=' instead of '=!'?") }
invalid_ann_assign_target[expr_ty]:
| list
| tuple
Expand Down
50 changes: 50 additions & 0 deletions Lib/test/test_syntax.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3505,6 +3505,56 @@ def test_ifexp_body_stmt_else_stmt(self):
]:
self._check_error(f"x = {lhs_stmt} if 1 else {rhs_stmt}", msg)

def test_diamond_operator(self):
self._check_error(
"1 < > 2",
"Maybe you meant '!=' instead of '<>'?",
lineno=1,
end_lineno=1,
offset=3,
end_offset=6,
)

def test_triple_equal(self):
self._check_error(
"a === b",
"Maybe you meant '==' instead of '==='?",
lineno=1,
end_lineno=1,
offset=3,
end_offset=6,
)

def test_eq_lt_typo(self):
self._check_error(
"a =< b",
"Maybe you meant '<=' instead of '=<'?",
lineno=1,
end_lineno=1,
offset=3,
end_offset=5,
)

def test_eq_gt_typo(self):
self._check_error(
"a => b",
"Maybe you meant '>=' instead of '=>'?",
lineno=1,
end_lineno=1,
offset=3,
end_offset=5,
)

def test_eq_bang_typo(self):
self._check_error(
"a =! b",
"Maybe you meant '!=' instead of '=!'?",
lineno=1,
end_lineno=1,
offset=3,
end_offset=5,
)


class LazyImportRestrictionTestCase(SyntaxErrorTestCase):
"""Test syntax restrictions for lazy imports."""
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-12-03-41-39.gh-issue-151303.mzlJxi.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Improve :exc:`SyntaxError` message for ``===``, ``=<``, ``=>``, ``=!``, and ``<>`` operators, suggesting ``==``, ``<=``, ``>=``, ``!=``, and ``!=`` respectively.
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