flake8-use-fstring
Flake8 plugin for string formatting style.
Decision gist · record as of 2026-08-14
Yes, if you are actively modernizing a codebase to f-strings and already use flake8. The plugin is lightweight, has no dependencies, and integrates seamlessly. However, maintenance is dormant (last release 1479 days ago), so compatibility with very recent flake8 versions is uncertain—verify it works with your flake8 version before relying on it in CI/CD. For new projects, consider whether a more actively maintained linter rule might be preferable.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python >= 3.6 and an existing flake8 installation; the plugin only works as a flake8 extension, not standalone.
- High install friction due to being a flake8 plugin with no runtime dependencies but requiring integration into an existing flake8 setup.
- Last release was 1479 days ago; repository is dormant but not archived, so maintenance is stalled.
License · maintenance · safety
permissive license (permissive) — Licensed under MIT (permissive), so no restrictions on use or modification in commercial or private projects.
last release 2022-07-27 (1479 days) · last repo commit 2023-11-07 · 50 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 425,296 downloads/mo, #6,759 on PyPI
Alternatives
Verify before relying
pip install flake8-use-fstring
# Then run flake8 as normal; the plugin auto-registers
flake8 myfile.py
# Configure in .flake8:
# [flake8]
# percent-greedy = 0
# format-greedy = 0- Whether the plugin remains compatible with recent flake8 versions given the dormant maintenance status.
- Real-world false-positive rate at greedy levels 1 and 2 beyond the documented examples.
What it is and what it does
flake8-use-fstring is a flake8 linter plugin that flags instances of % formatting and .format() method calls in Python code, pushing developers toward f-strings. It reports three error codes: FS001 for % formatting, FS002 for .format usage, and FS003 (disabled by default) for strings that look like they should be f-strings but lack the f prefix. The plugin works by scanning logical lines and checking whether the value before % or .format is a string literal, with configurable greedy levels (0–2) to control sensitivity and reduce false positives.
The plugin integrates directly into flake8's workflow and requires no runtime dependencies. It supports Python 3.6 and later, matching the version f-strings were introduced. Configuration is done via command-line flags or a .flake8 config file. The main trade-off is that without type information, the plugin cannot always determine whether a value is truly a string, so higher greedy levels may report false positives on non-string values.
Use it for
- Enforce f-string adoption across a codebase during a Python modernization effort.
- Catch legacy string formatting in code reviews as part of a flake8 linting pipeline.
- Configure FS003 to flag strings with {} that are missing the f prefix, catching incomplete f-string migrations.
- Use greedy level 0 (default) in strict projects where only obvious string literals should trigger warnings.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you are actively modernizing a codebase to f-strings and already use flake8.
The plugin is lightweight, has no dependencies, and integrates seamlessly. However, maintenance is dormant (last release 1479 days ago), so compatibility with very recent flake8 versions is uncertain—verify it works with your flake8 version before relying on it in CI/CD. For new projects, consider whether a more actively maintained linter rule might be preferable.
Install
flake8-use-fstring on PyPI
Before you install
High install friction due to being a flake8 plugin with no runtime dependencies but requiring integration into an existing flake8 setup. Last release was 1479 days ago; repository is dormant but not archived, so maintenance is stalled.
Requires Python >= 3.6 and an existing flake8 installation; the plugin only works as a flake8 extension, not standalone.
License in practice
Licensed under MIT (permissive), so no restrictions on use or modification in commercial or private projects.
Quickstart
pip install flake8-use-fstring
# Then run flake8 as normal; the plugin auto-registers
flake8 myfile.py
# Configure in .flake8:
# [flake8]
# percent-greedy = 0
# format-greedy = 0Verify before relying
- Whether the plugin remains compatible with recent flake8 versions given the dormant maintenance status.
- Real-world false-positive rate at greedy levels 1 and 2 beyond the documented examples.
Package facts
| License | permissive license permissive |
| Python support | Supports the current Python release >=3.6 |
| Install friction | High. Source build required |
| Runtime dependencies | None |
| Maintenance | Dormant 1,479 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 425,296 / month, #6,759 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 3 - AlphaIntended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseProgramming Language :: PythonProgramming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.6Programming Language :: Python :: 3.7Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Topic :: Software Development :: Libraries :: Python ModulesTopic :: Software Development :: Quality Assurance |
Evidence: flake8-use-fstring-1.4.tar.gz
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