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bpo-42381: Allow walrus in set literals and set comprehensions #23332

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Merged
merged 1 commit into from
Nov 17, 2020
Merged

bpo-42381: Allow walrus in set literals and set comprehensions #23332

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5 changes: 2 additions & 3 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -311,7 +311,6 @@ block[asdl_stmt_seq*] (memo):
| simple_stmt
| invalid_block

expressions_list[asdl_expr_seq*]: a[asdl_expr_seq*]=','.star_expression+ [','] { a }
star_expressions[expr_ty]:
| a=star_expression b=(',' c=star_expression { c })+ [','] {
_Py_Tuple(CHECK(asdl_expr_seq*, _PyPegen_seq_insert_in_front(p, a, b)), Load, EXTRA) }
Expand Down Expand Up @@ -519,9 +518,9 @@ group[expr_ty]:
genexp[expr_ty]:
| '(' a=expression ~ b=for_if_clauses ')' { _Py_GeneratorExp(a, b, EXTRA) }
| invalid_comprehension
set[expr_ty]: '{' a=expressions_list '}' { _Py_Set(a, EXTRA) }
set[expr_ty]: '{' a=star_named_expressions '}' { _Py_Set(a, EXTRA) }
setcomp[expr_ty]:
| '{' a=expression ~ b=for_if_clauses '}' { _Py_SetComp(a, b, EXTRA) }
| '{' a=named_expression ~ b=for_if_clauses '}' { _Py_SetComp(a, b, EXTRA) }
| invalid_comprehension
dict[expr_ty]:
| '{' a=[double_starred_kvpairs] '}' {
Expand Down
60 changes: 57 additions & 3 deletions Lib/test/test_named_expressions.py
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Expand Up @@ -113,7 +113,7 @@ def test_named_expression_invalid_in_class_body(self):
"assignment expression within a comprehension cannot be used in a class body"):
exec(code, {}, {})

def test_named_expression_invalid_rebinding_comprehension_iteration_variable(self):
def test_named_expression_invalid_rebinding_list_comprehension_iteration_variable(self):
cases = [
("Local reuse", 'i', "[i := 0 for i in range(5)]"),
("Nested reuse", 'j', "[[(j := 0) for i in range(5)] for j in range(5)]"),
Expand All @@ -130,7 +130,7 @@ def test_named_expression_invalid_rebinding_comprehension_iteration_variable(sel
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {})

def test_named_expression_invalid_rebinding_comprehension_inner_loop(self):
def test_named_expression_invalid_rebinding_list_comprehension_inner_loop(self):
cases = [
("Inner reuse", 'j', "[i for i in range(5) if (j := 0) for j in range(5)]"),
("Inner unpacking reuse", 'j', "[i for i in range(5) if (j := 0) for j, k in [(0, 1)]]"),
Expand All @@ -145,7 +145,7 @@ def test_named_expression_invalid_rebinding_comprehension_inner_loop(self):
with self.assertRaisesRegex(SyntaxError, msg):
exec(f"lambda: {code}", {}) # Function scope

def test_named_expression_invalid_comprehension_iterable_expression(self):
def test_named_expression_invalid_list_comprehension_iterable_expression(self):
cases = [
("Top level", "[i for i in (i := range(5))]"),
("Inside tuple", "[i for i in (2, 3, i := range(5))]"),
Expand All @@ -167,6 +167,60 @@ def test_named_expression_invalid_comprehension_iterable_expression(self):
with self.assertRaisesRegex(SyntaxError, msg):
exec(f"lambda: {code}", {}) # Function scope

def test_named_expression_invalid_rebinding_set_comprehension_iteration_variable(self):
cases = [
("Local reuse", 'i', "{i := 0 for i in range(5)}"),
("Nested reuse", 'j', "{{(j := 0) for i in range(5)} for j in range(5)}"),
("Reuse inner loop target", 'j', "{(j := 0) for i in range(5) for j in range(5)}"),
("Unpacking reuse", 'i', "{i := 0 for i, j in {(0, 1)}}"),
("Reuse in loop condition", 'i', "{i+1 for i in range(5) if (i := 0)}"),
("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)}"),
]
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, {}, {})

def test_named_expression_invalid_rebinding_set_comprehension_inner_loop(self):
cases = [
("Inner reuse", 'j', "{i for i in range(5) if (j := 0) for j in range(5)}"),
("Inner unpacking reuse", 'j', "{i for i in range(5) if (j := 0) for j, k in {(0, 1)}}"),
]
for case, target, code in cases:
msg = f"comprehension inner loop cannot rebind assignment expression target '{target}'"
with self.subTest(case=case):
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_set_comprehension_iterable_expression(self):
cases = [
("Top level", "{i for i in (i := range(5))}"),
("Inside tuple", "{i for i in (2, 3, i := range(5))}"),
("Inside list", "{i for i in {2, 3, i := range(5)}}"),
("Different name", "{i for i in (j := range(5))}"),
("Lambda expression", "{i for i in (lambda:(j := range(5)))()}"),
("Inner loop", "{i for i in range(5) for j in (i := range(5))}"),
("Nested comprehension", "{i for i in {j for j in (k := range(5))}}"),
("Nested comprehension condition", "{i for i in {j for j in range(5) if (j := True)}}"),
("Nested comprehension body", "{i for i in {(j := True) for j in range(5)}}"),
]
msg = "assignment expression cannot be used in a comprehension iterable expression"
for case, code in cases:
with self.subTest(case=case):
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


class NamedExpressionAssignmentTest(unittest.TestCase):

Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-11-16-23-45-56.bpo-42381.G4AWxL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Allow assignment expressions in set literals and set comprehensions as per
PEP 572. Patch by Pablo Galindo.
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