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gh-140344: ast: Add deprecation warnings #140345

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gh-140344: ast: Add deprecation warnings
jepler Oct 20, 2025
7c57211
NEWS: Finish detailing the change to the ast module.
jepler Oct 21, 2025
dc5abf8
Doc: further document ast deprecations & removals
jepler Oct 21, 2025
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23 changes: 22 additions & 1 deletion Lib/ast.py
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,6 @@
"""
from _ast import *


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Please revert unrelated changes.

def parse(source, filename='<unknown>', mode='exec', *,
type_comments=False, feature_version=None, optimize=-1):
"""
Expand Down Expand Up @@ -607,9 +606,13 @@ def __new__(cls, dims=(), **kwargs):

def _dims_getter(self):
"""Deprecated. Use elts instead."""
import warnings
warnings._deprecated(f"ast.Tuple.dims", remove=(3, 20))
return self.elts

def _dims_setter(self, value):
import warnings
warnings._deprecated(f"ast.Tuple.dims", remove=(3, 20))
self.elts = value

Tuple.dims = property(_dims_getter, _dims_setter)
Expand Down Expand Up @@ -689,5 +692,23 @@ def main(args=None):
print(dump(tree, include_attributes=args.include_attributes,
indent=args.indent, show_empty=args.show_empty))

_deprecated = {
'slice': globals().pop("slice"),
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Note this means from ast import * will no longer pick these up. That's probably OK for 3.15 but let's mention it in docs.

'Index': globals().pop("Index"),
'ExtSlice': globals().pop("ExtSlice"),
'Suite': globals().pop("Suite"),
'AugLoad': globals().pop("AugLoad"),
'AugStore': globals().pop("AugStore"),
'Param': globals().pop("Param")
}

def __getattr__(attr):
if val := _deprecated.get(attr, None):
import warnings
warnings._deprecated(f"ast.{attr}", remove=(3, 20))
globals()[attr] = val
return val
raise AttributeError(f"module 'ast' has no attribute {attr!r}")

if __name__ == '__main__':
main()
28 changes: 28 additions & 0 deletions Lib/test/test_ast/test_ast.py
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Original file line number Diff line number Diff line change
Expand Up @@ -502,6 +502,12 @@ def test_classattrs(self):
self.assertIs(ast.Constant(None).value, None)
self.assertIs(ast.Constant(...).value, ...)

with self.assertWarns(DeprecationWarning):
ast.Tuple().dims

with self.assertWarns(DeprecationWarning):
ast.Tuple().dims = 3

def test_constant_subclasses(self):
class N(ast.Constant):
def __init__(self, *args, **kwargs):
Expand Down Expand Up @@ -1124,6 +1130,28 @@ def test_tstring(self):
self.assertIsInstance(tree.body[0].value.values[0], ast.Constant)
self.assertIsInstance(tree.body[0].value.values[1], ast.Interpolation)

def test_deprecated(self):
with self.assertWarns(DeprecationWarning):
ast.slice

with self.assertWarns(DeprecationWarning):
ast.Index

with self.assertWarns(DeprecationWarning):
ast.ExtSlice

with self.assertWarns(DeprecationWarning):
ast.Suite

with self.assertWarns(DeprecationWarning):
ast.AugLoad

with self.assertWarns(DeprecationWarning):
ast.AugStore

with self.assertWarns(DeprecationWarning):
ast.Param


class CopyTests(unittest.TestCase):
"""Test copying and pickling AST nodes."""
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2025-10-20-09-12-18.gh-issue-140344.WjbYg-.rst
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@@ -0,0 +1,3 @@
The classes ``ast.Suite``, ``ast.AugLoad``, ``ast.AugStore``, and
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This only lists four of the seven things deprecated. It also doesn't mention the .dims attribute.

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added, thanks.

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Any migration guidance if anyone still uses these?

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You can find discussion around the original deprecations, e.g., #84169 but I didn't find any specific migration advice.

An ast produced by ast.parse will never include instances of these classes.

The implementation of all the removed classes are pretty trivial so if you need them for some reason you can probably just copy them. e.g., AugLoad has no body beyond a docstring.

  class AugLoad(expr_context):
      """Deprecated AST node class.  Unused in Python 3."""

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Yeah there's no good use for them. Most likely if people are using them, it's just some code that does something for all AST nodes, and they should simply delete the code handling these nodes. But that's guesswork.

``ast.Param``, deprecated since Python 3.9, now issue deprecation warnings
on use. They are now scheduled for removal in Python 3.20.
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