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gh-87447: Fix walrus comprehension rebind checking (#100581) 

Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>
Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
This commit is contained in:
Nikita Sobolev 2023-01-09 01:51:29 +03:00 committed by GitHub
parent 8d69828092
commit bc0a686f82
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GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 92 additions and 3 deletions
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7
Doc/whatsnew/3.12.rst
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@ -182,6 +182,13 @@ Other Language Changes
arguments of any type instead of just :class:`bool` and :class:`int`.
(Contributed by Serhiy Storchaka in :gh:`60203`.)
* Variables used in the target part of comprehensions that are not stored to
can now be used in assignment expressions (``:=``).
For example, in ``[(b := 1) for a, b.prop in some_iter]``, the assignment to
``b`` is now allowed. Note that assigning to variables stored to in the target
part of comprehensions (like ``a``) is still disallowed, as per :pep:`572`.
(Contributed by Nikita Sobolev in :gh:`100581`.)
New Modules
===========

80
Lib/test/test_named_expressions.py
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@ -114,6 +114,69 @@ class NamedExpressionInvalidTest(unittest.TestCase):
"assignment expression within a comprehension cannot be used in a class body"):
exec(code, {}, {})
def test_named_expression_valid_rebinding_iteration_variable(self):
# This test covers that we can reassign variables
# that are not directly assigned in the
# iterable part of a comprehension.
cases = [
# Regression tests from https://github.com/python/cpython/issues/87447
("Complex expression: c",
"{0}(c := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
("Complex expression: d",
"{0}(d := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
("Complex expression: e",
"{0}(e := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
("Complex expression: f",
"{0}(f := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
("Complex expression: g",
"{0}(g := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
("Complex expression: h",
"{0}(h := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
("Complex expression: i",
"{0}(i := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
("Complex expression: j",
"{0}(j := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
]
for test_case, code in cases:
for lpar, rpar in [('(', ')'), ('[', ']'), ('{', '}')]:
code = code.format(lpar, rpar)
with self.subTest(case=test_case, lpar=lpar, rpar=rpar):
# Names used in snippets are not defined,
# but we are fine with it: just must not be a SyntaxError.
# Names used in snippets are not defined,
# but we are fine with it: just must not be a SyntaxError.
with self.assertRaises(NameError):
exec(code, {}) # Module scope
with self.assertRaises(NameError):
exec(code, {}, {}) # Class scope
exec(f"lambda: {code}", {}) # Function scope
def test_named_expression_invalid_rebinding_iteration_variable(self):
# This test covers that we cannot reassign variables
# that are directly assigned in the iterable part of a comprehension.
cases = [
# Regression tests from https://github.com/python/cpython/issues/87447
("Complex expression: a", "a",
"{0}(a := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
("Complex expression: b", "b",
"{0}(b := 1) for a, (*b, c[d+e::f(g)], h.i) in j{1}"),
]
for test_case, target, code in cases:
msg = f"assignment expression cannot rebind comprehension iteration variable '{target}'"
for lpar, rpar in [('(', ')'), ('[', ']'), ('{', '}')]:
code = code.format(lpar, rpar)
with self.subTest(case=test_case, lpar=lpar, rpar=rpar):
# Names used in snippets are not defined,
# but we are fine with it: just must not be a SyntaxError.
# Names used in snippets are not defined,
# but we are fine with it: just must not be a SyntaxError.
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}) # Module scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {}) # Class scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(f"lambda: {code}", {}) # Function scope
def test_named_expression_invalid_rebinding_list_comprehension_iteration_variable(self):
cases = [
("Local reuse", 'i', "[i := 0 for i in range(5)]"),
@ -129,7 +192,11 @@ class NamedExpressionInvalidTest(unittest.TestCase):
msg = f"assignment expression cannot rebind comprehension iteration variable '{target}'"
with self.subTest(case=case):
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {})
exec(code, {}) # Module scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {}) # Class scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(f"lambda: {code}", {}) # Function scope
def test_named_expression_invalid_rebinding_list_comprehension_inner_loop(self):
cases = [
@ -178,12 +245,21 @@ class NamedExpressionInvalidTest(unittest.TestCase):
("Unreachable reuse", 'i', "{False or (i:=0) for i in range(5)}"),
("Unreachable nested reuse", 'i',
"{(i, j) for i in range(5) for j in range(5) if True or (i:=10)}"),
# Regression tests from https://github.com/python/cpython/issues/87447
("Complex expression: a", "a",
"{(a := 1) for a, (*b, c[d+e::f(g)], h.i) in j}"),
("Complex expression: b", "b",
"{(b := 1) for a, (*b, c[d+e::f(g)], h.i) in j}"),
]
for case, target, code in cases:
msg = f"assignment expression cannot rebind comprehension iteration variable '{target}'"
with self.subTest(case=case):
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {})
exec(code, {}) # Module scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {}) # Class scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(f"lambda: {code}", {}) # Function scope
def test_named_expression_invalid_rebinding_set_comprehension_inner_loop(self):
cases = [

5
Misc/NEWS.d/next/Core and Builtins/2022-12-28-15-02-53.gh-issue-87447.7-aekA.rst Normal file
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@ -0,0 +1,5 @@
Fix :exc:`SyntaxError` on comprehension rebind checking with names that are
not actually redefined.
Now reassigning ``b`` in ``[(b := 1) for a, b.prop in some_iter]`` is allowed.
Reassigning ``a`` is still disallowed as per :pep:`572`.

3
Python/symtable.c
View File

@ -1488,7 +1488,8 @@ symtable_extend_namedexpr_scope(struct symtable *st, expr_ty e)
*/
if (ste->ste_comprehension) {
long target_in_scope = _PyST_GetSymbol(ste, target_name);
if (target_in_scope & DEF_COMP_ITER) {
if ((target_in_scope & DEF_COMP_ITER) &&
(target_in_scope & DEF_LOCAL)) {
PyErr_Format(PyExc_SyntaxError, NAMED_EXPR_COMP_CONFLICT, target_name);
PyErr_RangedSyntaxLocationObject(st->st_filename,
e->lineno,