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GeezerVison is showing github.com — gh-153568: Use a managed dict for AST nodes by lysnikolaou · Pull Request #160616 · python/cpython

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@lysnikolaou

@lysnikolaou lysnikolaou commented Oct 24, 2026 •
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AST nodes had an explicit __dict__ slot, so every node built by ast.parse allocated its own dict. With Py_TPFLAGS_MANAGED_DICT, node attributes are stored as inline values with shared keys instead.

ast.parse is ~15.8% faster, walking trees is ~15.9% faster, and the memory used by the AST trees is reduced by ~51.6%.

  • Issue: Speed up the parser #153568

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@lysnikolaou
pythongh-153568: Use a managed dict for AST nodes
9ba7fbe 
AST nodes had an explicit `__dict__`` slot, so every node built by
`ast.parse` allocated its own dict. With Py_TPFLAGS_MANAGED_DICT,
node attributes are stored as inline values with shared keys instead.

`ast.parse` is ~15.8% faster, walking trees is ~15.9% faster, and
the memory used by the AST trees is reduced by ~51.6%.
@lysnikolaou
lysnikolaou requested review from Eclips4, pablogsal and tomasr8 as code owners October 24, 2026 19:00
@bedevere-app bedevere-app Bot added awaiting core review type-feature A feature request or enhancement labels Oct 24, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Oct 24, 2026
Speed up the parser #153568
Open
@lysnikolaou
Add news blurb
1a69802
pablogsal
pablogsal approved these changes Oct 25, 2026
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Fucking amazing!

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Oct 25, 2026
@lysnikolaou
lysnikolaou merged commit aa0e410 into python:main Oct 25, 2026
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@bedevere-app bedevere-app Bot removed the awaiting merge label Oct 25, 2026
@lysnikolaou
lysnikolaou deleted the ast-node-inline-values branch October 25, 2026 17:08
This was referenced Nov 2, 2026
Use a managed dict for the _io types #161184
Open
gh-161184: Use a managed dict and weakref list for the _io types #161236
Open
@vstinner vstinner mentioned this pull request Nov 4, 2026
test_ast: test_nodes_have_inline_values() fails when test_ast is run twice #161354
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@vstinner

vstinner commented Nov 4, 2026

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This change introduced a regression: test_ast now fails when it's run twice, see issue gh-161354.
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@vstinner

vstinner commented Nov 4, 2026

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Nice optimization by the way :-)
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@sobolevn sobolevn mentioned this pull request Nov 4, 2026
Remove duplicate NEWS entry #161361
Merged
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@pablogsal pablogsal pablogsal approved these changes
@Eclips4 Eclips4 Awaiting requested review from Eclips4 Eclips4 is a code owner
@tomasr8 tomasr8 Awaiting requested review from tomasr8 tomasr8 is a code owner

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3 participants

@lysnikolaou @vstinner @pablogsal
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