https://github.com/python/cpython/commit/4d0849426f4c6862e50658c4e35341ffb5ab288b
commit: 4d0849426f4c6862e50658c4e35341ffb5ab288b
branch: main
author: George Ogden <[email protected]>
committer: JelleZijlstra <[email protected]>
date: 2025-10-23T13:56:05Z
summary:
gh-138774: use `value` to `ast.unparse` code when `str` is `None` in
`ast.Interpolation` (#139415)
files:
A Misc/NEWS.d/next/Library/2025-10-23-12-12-22.gh-issue-138774.mnh2gU.rst
M Doc/library/ast.rst
M Lib/_ast_unparse.py
M Lib/test/test_unparse.py
diff --git a/Doc/library/ast.rst b/Doc/library/ast.rst
index ea3ec7d95dc45d..494621672171f2 100644
--- a/Doc/library/ast.rst
+++ b/Doc/library/ast.rst
@@ -363,6 +363,11 @@ Literals
function call).
This has the same meaning as ``FormattedValue.value``.
* ``str`` is a constant containing the text of the interpolation expression.
+
+ If ``str`` is set to ``None``, then ``value`` is used to generate code
+ when calling :func:`ast.unparse`. This no longer guarantees that the
+ generated code is identical to the original and is intended for code
+ generation.
* ``conversion`` is an integer:
* -1: no conversion
diff --git a/Lib/_ast_unparse.py b/Lib/_ast_unparse.py
index 16cf56f62cc1e5..1c8741b5a55483 100644
--- a/Lib/_ast_unparse.py
+++ b/Lib/_ast_unparse.py
@@ -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)
@@ -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)
diff --git a/Lib/test/test_unparse.py b/Lib/test/test_unparse.py
index 0d6b05bc660b76..35e4652a87b423 100644
--- a/Lib/test/test_unparse.py
+++ b/Lib/test/test_unparse.py
@@ -206,6 +206,97 @@ def test_tstrings(self):
self.check_ast_roundtrip("t'foo'")
self.check_ast_roundtrip("t'foo {bar}'")
self.check_ast_roundtrip("t'foo {bar!s:.2f}'")
+ self.check_ast_roundtrip("t'{a + b}'")
+ self.check_ast_roundtrip("t'{a + b:x}'")
+ self.check_ast_roundtrip("t'{a + b!s}'")
+ self.check_ast_roundtrip("t'{ {a}}'")
+ self.check_ast_roundtrip("t'{ {a}=}'")
+ self.check_ast_roundtrip("t'{{a}}'")
+ 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'")
@@ -813,15 +904,6 @@ def test_type_params(self):
self.check_ast_roundtrip("def f[T: int = int, **P = int, *Ts =
*int]():\n pass")
self.check_ast_roundtrip("class C[T: int = int, **P = int, *Ts =
*int]():\n pass")
- def test_tstr(self):
- self.check_ast_roundtrip("t'{a + b}'")
- self.check_ast_roundtrip("t'{a + b:x}'")
- self.check_ast_roundtrip("t'{a + b!s}'")
- self.check_ast_roundtrip("t'{ {a}}'")
- self.check_ast_roundtrip("t'{ {a}=}'")
- self.check_ast_roundtrip("t'{{a}}'")
- self.check_ast_roundtrip("t''")
-
class ManualASTCreationTestCase(unittest.TestCase):
"""Test that AST nodes created without a type_params field unparse
correctly."""
diff --git
a/Misc/NEWS.d/next/Library/2025-10-23-12-12-22.gh-issue-138774.mnh2gU.rst
b/Misc/NEWS.d/next/Library/2025-10-23-12-12-22.gh-issue-138774.mnh2gU.rst
new file mode 100644
index 00000000000000..e12f789e674454
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-10-23-12-12-22.gh-issue-138774.mnh2gU.rst
@@ -0,0 +1,2 @@
+:func:`ast.unparse` now generates full source code when handling
+:class:`ast.Interpolation` nodes that do not have a specified source.
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