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gh-153171: Produce specialized syntax errors in more cases #153193

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18 changes: 17 additions & 1 deletion Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -783,6 +783,7 @@ inversion[expr_ty] (memo):
# --------------------

comparison[expr_ty]:
| invalid_comparison
| a=bitwise_or b=compare_op_bitwise_or_pair+ {
_PyAST_Compare(
a,
Expand Down Expand Up @@ -825,6 +826,7 @@ bitwise_or[expr_ty]:

bitwise_xor[expr_ty]:
| a=bitwise_xor '^' b=bitwise_and { _PyAST_BinOp(a, BitXor, b, EXTRA) }
| invalid_bitwise_xor
| bitwise_and

bitwise_and[expr_ty]:
Expand All @@ -835,6 +837,7 @@ bitwise_and[expr_ty]:
shift_expr[expr_ty]:
| a=shift_expr '<<' b=sum { _PyAST_BinOp(a, LShift, b, EXTRA) }
| a=shift_expr '>>' b=sum { _PyAST_BinOp(a, RShift, b, EXTRA) }
| invalid_shift_expr
| sum

# Arithmetic operators
Expand Down Expand Up @@ -863,6 +866,7 @@ factor[expr_ty] (memo):

power[expr_ty]:
| a=await_primary '**' b=factor { _PyAST_BinOp(a, Pow, b, EXTRA) }
| invalid_power
| await_primary

# Primary elements
Expand Down Expand Up @@ -1373,7 +1377,7 @@ invalid_parameters:
| param_maybe_default+ '/' a='*' {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "expected comma between / and *") }
invalid_default:
| a='=' &(')'|',') { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "expected default value expression") }
| a='=' &(')'|','|':') { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "expected default value expression") }
invalid_star_etc:
| a='*' (')' | ',' (')' | '**')) { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "named parameters must follow bare *") }
| '*' ',' TYPE_COMMENT { RAISE_SYNTAX_ERROR("bare * has associated type comment") }
Expand Down Expand Up @@ -1640,21 +1644,33 @@ invalid_arithmetic:
| sum ('+'|'-'|'*'|'/'|'%'|'//'|'@') a='not' b=inversion { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }
invalid_factor:
| ('+' | '-' | '~') a='not' b=factor { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }
invalid_comparison:
| bitwise_or ('=='|'!='|'<='|'<'|'>='|'>') a='not' b=inversion { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }
invalid_bitwise_xor:
| bitwise_xor '^' a='not' b=inversion { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }
invalid_shift_expr:
| shift_expr ('<<'|'>>') a='not' b=inversion { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }
invalid_power:
| await_primary '**' a='not' b=inversion { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }

invalid_type_params:
| '[' ','.type_param+ a='=' &(']' | ',') {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "expected default value expression") }
| '[' token=']' {
RAISE_SYNTAX_ERROR_STARTING_FROM(
token,
"Type parameter list cannot be empty")}

invalid_bitwise_and:
| bitwise_and '&' a='not' b=inversion { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }
| a=bitwise_and b='&' c='&' {
_PyPegen_tokens_are_adjacent(b, c)
? RAISE_SYNTAX_ERROR_KNOWN_RANGE(b, c, "invalid syntax. Maybe you meant 'and' or '&' instead of '&&'?")
: NULL
}

invalid_bitwise_or:
| bitwise_or '|' a='not' b=inversion { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "'not' after an operator must be parenthesized") }
| a=bitwise_or b='|' c='|' {
_PyPegen_tokens_are_adjacent(b, c)
? RAISE_SYNTAX_ERROR_KNOWN_RANGE(b, c, "invalid syntax. Maybe you meant 'or' or '|' instead of '||'?")
Expand Down
56 changes: 56 additions & 0 deletions Lib/test/test_syntax.py
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Original file line number Diff line number Diff line change
Expand Up @@ -657,6 +657,10 @@
Traceback (most recent call last):
SyntaxError: expected default value expression

>>> lambda a,d=: None
Traceback (most recent call last):
SyntaxError: expected default value expression

>>> lambda a,d=3,c: None
Traceback (most recent call last):
SyntaxError: parameter without a default follows parameter with a default
Expand Down Expand Up @@ -2284,6 +2288,38 @@
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

>>> 1 << not 2
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

>>> 1 >> not 2
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

>>> 1 & not 2
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

>>> 1 ^ not 2
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

>>> 1 | not 2
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

>>> 1 < not 2
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

>>> 1 == not 2
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

>>> 2 ** not 2
Traceback (most recent call last):
SyntaxError: 'not' after an operator must be parenthesized

# Check that we don't introduce misleading errors
>>> not 1 */ 2
Traceback (most recent call last):
Expand Down Expand Up @@ -2588,6 +2624,26 @@ def f(x: *b)
...
SyntaxError: Type parameter list cannot be empty

>>> type A[T=] = int
Traceback (most recent call last):
...
SyntaxError: expected default value expression

>>> def f[T: int =](): ...
Traceback (most recent call last):
...
SyntaxError: expected default value expression

>>> class A[*T=]: ...
Traceback (most recent call last):
...
SyntaxError: expected default value expression

>>> class A[**T=, U]: ...
Traceback (most recent call last):
...
SyntaxError: expected default value expression

>>> class A[]: ...
Traceback (most recent call last):
...
Expand Down
8 changes: 8 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-07-06-21-00-00.gh-issue-153171.errloc2.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
Produce specialized syntax error messages in more cases
where a generic or unrelated error was previously reported:
for ``not`` after shift, bitwise, comparison and power operators
(such as ``1 << not x``),
for a missing parameter default value in lambda expressions
(such as ``lambda x=: 0``),
and for a missing type parameter default value
(such as ``def f[T=](): pass``).
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