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gh-138774: use value to ast.unparse code when str is None in ast.Interpolation #139415

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Merged
JelleZijlstra merged 11 commits into from
Oct 23, 2025
Merged

gh-138774: use value to ast.unparse code when str is None in ast.Interpolation #139415

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58c8c1a
Put all tstring tests in the same method
George-Ogden Sep 29, 2025
e62ae02
Use `value` field to generate code when `None` in `str` field of `ast…
George-Ogden Sep 29, 2025
5ab2512
Update documentation to describe `None` in `ast.Interpolation`
George-Ogden Sep 29, 2025
0fa0574
Merge branch 'main' into fix-issue-138774
George-Ogden Sep 29, 2025
bb70f1c
Merge branch 'main' into fix-issue-138774
George-Ogden Sep 29, 2025
3731763
Wrap line width to 79 characters
George-Ogden Sep 29, 2025
78494b2
Merge branch 'fix-issue-138774' of github.com:George-Ogden/cpython in…
George-Ogden Sep 29, 2025
aa7feb1
Include indent on wrapped lines
George-Ogden Sep 29, 2025
98e155b
Merge branch 'main' into fix-issue-138774
George-Ogden Oct 21, 2025
33714ad
Merge branch 'main' into fix-issue-138774
George-Ogden Oct 23, 2025
4b55278
Add NEWS entry
George-Ogden Oct 23, 2025
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Use value field to generate code when None in str field of `ast… 
….Interpolation`
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@George-Ogden
George-Ogden committed Sep 29, 2025
commit e62ae028c4396e78c90fd28b759882bb707667c2
7 changes: 4 additions & 3 deletions Lib/_ast_unparse.py
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Original file line number Diff line number Diff line change
Expand Up @@ -658,9 +658,9 @@ def _unparse_interpolation_value(self, inner):
unparser.set_precedence(_Precedence.TEST.next(), inner)
return unparser.visit(inner)

def _write_interpolation(self, node, is_interpolation=False):
def _write_interpolation(self, node, use_str_attr=False):
with self.delimit("{", "}"):
if is_interpolation:
if use_str_attr:
expr = node.str
else:
expr = self._unparse_interpolation_value(node.value)
Expand All @@ -678,7 +678,8 @@ def visit_FormattedValue(self, node):
self._write_interpolation(node)

def visit_Interpolation(self, node):
self._write_interpolation(node, is_interpolation=True)
# If `str` is set to `None`, use the `value` to generate the source code.
self._write_interpolation(node, use_str_attr=node.str is not None)

def visit_Name(self, node):
self.write(node.id)
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82 changes: 82 additions & 0 deletions Lib/test/test_unparse.py
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Expand Up @@ -215,6 +215,88 @@ def test_tstrings(self):
self.check_ast_roundtrip("t''")
self.check_ast_roundtrip('t""')
self.check_ast_roundtrip("t'{(lambda x: x)}'")
self.check_ast_roundtrip("t'{t'{x}'}'")

def test_tstring_with_nonsensical_str_field(self):
# `value` suggests that the original code is `t'{test1}`, but `str` suggests otherwise
self.assertEqual(
ast.unparse(
ast.TemplateStr(
values=[
ast.Interpolation(
value=ast.Name(id="test1", ctx=ast.Load()), str="test2", conversion=-1
)
]
)
),
"t'{test2}'",
)

def test_tstring_with_none_str_field(self):
self.assertEqual(
ast.unparse(
ast.TemplateStr(
[ast.Interpolation(value=ast.Name(id="test1"), str=None, conversion=-1)]
)
),
"t'{test1}'",
)
self.assertEqual(
ast.unparse(
ast.TemplateStr(
[
ast.Interpolation(
value=ast.Lambda(
args=ast.arguments(args=[ast.arg(arg="x")]),
body=ast.Name(id="x"),
),
str=None,
conversion=-1,
)
]
)
),
"t'{(lambda x: x)}'",
)
self.assertEqual(
ast.unparse(
ast.TemplateStr(
values=[
ast.Interpolation(
value=ast.TemplateStr(
# `str` field kept here
[ast.Interpolation(value=ast.Name(id="x"), str="y", conversion=-1)]
),
str=None,
conversion=-1,
)
]
)
),
'''t"{t'{y}'}"''',
)
self.assertEqual(
ast.unparse(
ast.TemplateStr(
values=[
ast.Interpolation(
value=ast.TemplateStr(
[ast.Interpolation(value=ast.Name(id="x"), str=None, conversion=-1)]
),
str=None,
conversion=-1,
)
]
)
),
'''t"{t'{x}'}"''',
)
self.assertEqual(
ast.unparse(ast.TemplateStr(
[ast.Interpolation(value=ast.Constant(value="foo"), str=None, conversion=114)]
)),
'''t"{'foo'!r}"''',
)

def test_strings(self):
self.check_ast_roundtrip("u'foo'")
Expand Down