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GeezerVison is showing github.com — gh-77273: Better bytecodes for f-strings by markshannon · Pull Request #6132 · python/cpython

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markshannon commented Mar 17, 2018 •

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Simplify and speed up interpreter for f-strings.

tldr; Do work in the compiler instead of the interpreter.

Splits the FORMAT_VALUE opcode into CONVERT_VALUE, FORMAT_SIMPLE and FORMAT_WITH_SPEC.
The compiler can then emit the optimal sequence for each format expression.

The three new opcodes are much simpler than the one they replace, actually removing a few lines of code from the interpreter.

The CONVERT_VALUE is emitted only if a conversion is present.
In the standard library only (approx) 20% of f-strings include a conversion.

FORMAT_WITH_SPEC is emitted if a format specifier is present.
Otherwise FORMAT_SIMPLE is emitted.
In the standard library about 70% of format expressions can be formatted with just the simple (and fast)
FORMAT_SIMPLE opcode.

https://bugs.python.org/issue33092

Issue: The bytecode for f-string formatting is inefficient. #77273

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the-knights-who-say-ni added the CLA signed label

Mar 17, 2018

bedevere-bot added the awaiting review label

Mar 17, 2018

markshannon force-pushed the better-bytecode-fstring branch from 554c1b6 to d79893a Compare

March 17, 2018 13:08

berkerpeksag requested a review from ericvsmith

March 23, 2018 13:53

markshannon force-pushed the better-bytecode-fstring branch from 35dea3c to 6a88b26 Compare

May 6, 2019 16:10

alimcmaster1 commented Apr 11, 2020

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Any update on this @taleinat suggested sharing benchmarks here https://bugs.python.org/issue33092.

Otherwise due to lack of activity I think we can close this.

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markshannon force-pushed the better-bytecode-fstring branch from 6a88b26 to cc0f91e Compare

December 1, 2020 16:25

bluss mentioned this pull request

Jun 19, 2021

bpo-33092: The bytecode for f-string formatting is inefficient. faster-cpython/ideas#61

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markshannon force-pushed the better-bytecode-fstring branch from cc0f91e to 7c1f2a6 Compare

August 25, 2021 13:30

ezio-melotti removed the CLA signed label

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github-actions Bot commented Aug 16, 2022

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This PR is stale because it has been open for 30 days with no activity.

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github-actions Bot added the stale Stale PR or inactive for long period of time. label

Aug 16, 2022

markshannon mentioned this pull request

Sep 1, 2022

The bytecode for f-string formatting is inefficient. #77273

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markshannon mentioned this pull request

Feb 13, 2023

gh-101799: implement PREP_RERAISE_STAR as an intrinsic function #101800

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furkanonder commented May 11, 2023

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CC: @rhettinger @ambv

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github-actions Bot removed the stale Stale PR or inactive for long period of time. label

May 14, 2023

markshannon added 4 commits

June 5, 2023 09:03


          Avoid conditional stack effects when compiling f-strings.

3af4084


          Merge branch 'main' into better-bytecode-fstring

a84bd65


          Fix up magic number.

b6d7171


          Document new instructions.

62a3404

markshannon closed this

Jun 8, 2023

markshannon reopened this

Jun 8, 2023

markshannon requested review from brettcannon, ericsnowcurrently, iritkatriel, ncoghlan and warsaw as code owners

June 8, 2023 11:32

markshannon force-pushed the better-bytecode-fstring branch from 7c1f2a6 to 3af4084 Compare

June 8, 2023 11:34

markshannon commented Jun 8, 2023

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Updated to use the new bytecode definition format.

Removes the conditional stack effect, simplifying tooling around these instructions.

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iritkatriel commented Jun 8, 2023

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Looks like you missed out the doc update.

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brettcannon removed their request for review

June 8, 2023 21:04

markshannon added 2 commits

June 9, 2023 10:56


          Merge branch 'main' into better-bytecode-fstring

31385d1


          Merge branch 'main' into better-bytecode-fstring

641466c

markshannon commented Jun 12, 2023

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#105678

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gvanrossum changed the title ~~bpo-33092: Better bytecodes for f-strings~~ gh-77273: Better bytecodes for f-strings

Jun 12, 2023

iritkatriel reviewed

Jun 14, 2023

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Lib/dis.py

Comment on lines +507 to +508

		argval = (None, str, repr, ascii)[arg]
		argrepr = ('', 'str', 'repr', 'ascii')[arg]

iritkatriel Jun 8, 2023

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since oparg 0 isn't a thing (right?), maybe write this as:

Suggested change

	argval = (None, str, repr, ascii)[arg]
	argrepr = ('', 'str', 'repr', 'ascii')[arg]
	argval = (_, str, repr, ascii)[arg]
	argrepr = (_, 'str', 'repr', 'ascii')[arg]

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markshannon Jun 14, 2023

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What is _? We might not use the 0th item, but it still needs to be defined.

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iritkatriel Jun 14, 2023

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IIUC _ is the convention for ‘unused value’.

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markshannon Jun 14, 2023

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For lvalues, sure, but this is an rvalue.

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iritkatriel approved these changes

Jun 14, 2023

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bedevere-bot added awaiting merge and removed awaiting review labels

Jun 14, 2023

markshannon merged commit 1d857da into python:main

Jun 14, 2023

bedevere-bot removed the awaiting merge label

Jun 14, 2023

carljm added a commit to carljm/cpython that referenced this pull request

Jun 15, 2023


          Merge branch 'main' into modulelocals

166aca9

* main: (57 commits)
  pythongh-105831: Fix NEWS blurb from pythongh-105828 (python#105833)
  pythongh-105820: Fix tok_mode expression buffer in file & readline tokenizer (python#105828)
  pythongh-105751, test_ctypes: Remove disabled tests (python#105826)
  pythongh-105821: Use a raw f-string in test_httpservers.py (python#105822)
  pythongh-105751: Remove platform usage in test_ctypes (python#105819)
  pythongh-105751: Reenable disable test_ctypes tests (python#105818)
  pythongh-105751: Remove dead code in test_ctypes (python#105817)
  More reorganisation of the typing docs (python#105787)
  Improve docs for `typing.dataclass_transform` (python#105792)
  pythonGH-89812: Churn `pathlib.Path` test methods (python#105807)
  pythongh-105800: Issue SyntaxWarning in f-strings for invalid escape sequences (python#105801)
  pythongh-105751: Cleanup test_ctypes imports (python#105803)
  pythongh-105481: add HAS_JUMP flag to opcode metadata (python#105791)
  pythongh-105751: test_ctypes avoids the operator module (pythonGH-105797)
  pythongh-105751: test_ctypes: Remove @need_symbol decorator (pythonGH-105798)
  pythongh-104909: Implement conditional stack effects for macros (python#105748)
  pythongh-75905: Remove test_xmlrpc_net: skipped since 2017 (python#105796)
  pythongh-105481: Fix types and a bug for pseudos (python#105788)
  Update DSL docs for cases generator (python#105753)
  pythonGH-77273: Better bytecodes for f-strings (pythonGH-6132)
  ...

ShaharNaveh mentioned this pull request

Dec 2, 2025

Align f-string related bytecodes with 3.13 RustPython/RustPython#6321

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ShaharNaveh mentioned this pull request

Apr 25, 2026

Unused FVC_NONE definition #148986

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markshannon commented Mar 17, 2018 • edited by bedevere-bot Loading Uh oh! There was an error while loading. Please reload this page.

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markshannon commented Mar 17, 2018 •

edited by bedevere-bot

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