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bpo-42316: Allow unparenthesized walrus operator in indexes (GH-23317)

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Lysandros Nikolaou 2020-11-17 01:09:35 +02:00 committed by GitHub
parent cb3e5ed071
commit cae60187cf
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4 changed files with 29 additions and 7 deletions
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2
Grammar/python.gram
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@ -491,7 +491,7 @@ slices[expr_ty]:
| a[asdl_expr_seq*]=','.slice+ [','] { _Py_Tuple(a, Load, EXTRA) }
slice[expr_ty]:
| a=[expression] ':' b=[expression] c=[':' d=[expression] { d }] { _Py_Slice(a, b, c, EXTRA) }
| a=expression { a }
| a=named_expression { a }
atom[expr_ty]:
| NAME
| 'True' { _Py_Constant(Py_True, NULL, EXTRA) }

21
Lib/test/test_named_expressions.py
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@ -271,6 +271,27 @@ class NamedExpressionAssignmentTest(unittest.TestCase):
fib = {(c := a): (a := b) + (b := a + c) - b for __ in range(6)}
self.assertEqual(fib, {1: 2, 2: 3, 3: 5, 5: 8, 8: 13, 13: 21})
def test_named_expression_assignment_17(self):
a = [1]
element = a[b:=0]
self.assertEqual(b, 0)
self.assertEqual(element, a[0])
def test_named_expression_assignment_18(self):
class TwoDimensionalList:
def __init__(self, two_dimensional_list):
self.two_dimensional_list = two_dimensional_list
def __getitem__(self, index):
return self.two_dimensional_list[index[0]][index[1]]
a = TwoDimensionalList([[1], [2]])
element = a[b:=0, c:=0]
self.assertEqual(b, 0)
self.assertEqual(c, 0)
self.assertEqual(element, a.two_dimensional_list[b][c])
class NamedExpressionScopeTest(unittest.TestCase):

1
Misc/NEWS.d/next/Core and Builtins/2020-11-16-17-30-03.bpo-42316._DdmpQ.rst Normal file
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@ -0,0 +1 @@
Allow an unparenthesized walrus in subscript indexes.

12
Parser/parser.c
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@ -10639,7 +10639,7 @@ slices_rule(Parser *p)
return _res;
}
// slice: expression? ':' expression? [':' expression?] | expression
// slice: expression? ':' expression? [':' expression?] | named_expression
static expr_ty
slice_rule(Parser *p)
{
@ -10701,18 +10701,18 @@ slice_rule(Parser *p)
D(fprintf(stderr, "%*c%s slice[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "expression? ':' expression? [':' expression?]"));
}
{ // expression
{ // named_expression
if (p->error_indicator) {
D(p->level--);
return NULL;
}
D(fprintf(stderr, "%*c> slice[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "expression"));
D(fprintf(stderr, "%*c> slice[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "named_expression"));
expr_ty a;
if (
(a = expression_rule(p)) // expression
(a = named_expression_rule(p)) // named_expression
)
{
D(fprintf(stderr, "%*c+ slice[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "expression"));
D(fprintf(stderr, "%*c+ slice[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "named_expression"));
_res = a;
if (_res == NULL && PyErr_Occurred()) {
p->error_indicator = 1;
@ -10723,7 +10723,7 @@ slice_rule(Parser *p)
}
p->mark = _mark;
D(fprintf(stderr, "%*c%s slice[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "expression"));
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "named_expression"));
}
_res = NULL;
done: