drop support for Python 3.9

[radoering]

Summary by Sourcery

Drop support for Python 3.9 and clean up code, tests, and CI configuration to target Python 3.10+.

Enhancements:

• Simplify temporary_directory helper to always use tempfile.TemporaryDirectory with ignore_cleanup_errors enabled for Python 3.10+.
• Modernize type annotations to use PEP 604 union syntax and updated collection ABC imports, and leverage pairwise iteration where available.
• Standardize subprocess helper to always run with locale-based text encoding.

Build:

• Raise the core package requires-python setting to ">=3.10,<4.0" and update the vendored project metadata accordingly.
• Remove the Python 3.9 target from linting configuration and related tooling.

CI:

• Update the test workflow matrix to drop Python 3.9 from CI runs.

Tests:

• Remove Python 3.9-specific temporary_directory tests and conditions, keeping a single test path for Python 3.10+ behavior.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Drops Python 3.9 support across code, tests, configuration, and CI, enabling use of Python 3.10+ features and simplifying version-dependent logic (notably around temporary directories, subprocess encoding, typing, and version constraint utilities).

Class diagram for updated typing constraints and aliases

classDiagram
    class BaseConstraint
    class VersionConstraint

    class SingleMarkerLike~T~
    class SingleMarkerConstraint {
        <<typevar>>
        bound BaseConstraint | VersionConstraint
    }

    SingleMarkerLike <|-- SingleMarker

    class SingleMarker {
        <<generic>> SingleMarkerLike~BaseConstraint | VersionConstraint~
    }

    class DependencyConstraint {
        <<typealias>>
        str | Mapping~str, Any~
    }

    class DependencyConfig {
        <<typealias>>
        Mapping~str, list~DependencyConstraint~ | DependencyConstraint~
    }

    class LocalSegmentType {
        <<typealias>>
        str | int | tuple~str | int, ...~ | None
    }

Loading

Flow diagram for updated temporary_directory helper

flowchart TD
    A[temporary_directory called] --> B[Set kwargs ignore_cleanup_errors true]
    B --> C[Create TemporaryDirectory with kwargs]
    C --> D[Yield Path of temporary directory name]
    D --> E[TemporaryDirectory context exits and cleans up directory]

Loading

File-Level Changes

Change	Details	Files
Simplify temporary_directory helper to Python 3.10+ behavior only and update tests accordingly.	Remove sys.version_info branching in temporary_directory, always using tempfile.TemporaryDirectory with ignore_cleanup_errors=True Delete legacy code path using tempfile.mkdtemp and robust_rmtree for Python 3.9 Unskip and rename tests that previously targeted Python 3.10-only behavior Remove tests that covered the Python 3.9-or-older temporary_directory code path Update temporary_directory tests to assume TemporaryDirectory is always used and cleanup is handled via ignore_cleanup_errors	src/poetry/core/utils/helpers.py tests/utils/test_helpers.py
Leverage Python 3.10+ typing features and simplify type annotations.	Replace Union[...] and Optional[...] annotations with PEP 604	unions in several modules Adjust generic TypeVar bound and class parameterization in markers to use
Clean up version-specific runtime logic now that minimum Python is 3.10.	Simplify subprocess_run helper to always use encoding='locale' with text=True, removing sys.version_info-based conditional Use itertools.pairwise in constraint_regions instead of manual zip over edges, relying on its availability in Python 3.10+ Add missing Callable import for TYPE_CHECKING usage in tests conftest	tests/testutils.py src/poetry/core/constraints/version/util.py tests/conftest.py
Update declared Python version support in packaging metadata, vendored configuration, and CI.	Bump requires-python from ">=3.9, <4.0" to ">=3.10, <4.0" in main pyproject.toml Remove Ruff target-version setting for py39, allowing tools to assume 3.10+ Update vendors/pyproject.toml requires-python from ">=3.9" to ">=3.10" Drop Python 3.9 from GitHub Actions test matrix so CI runs only on 3.10+ Regenerate or adjust lock files and vendor metadata consistent with the new minimum Python version	pyproject.toml .github/workflows/tests.yaml vendors/pyproject.toml poetry.lock vendors/poetry.lock src/poetry/core/_vendor/lark/LICENSE src/poetry/core/_vendor/lark/grammars/common.lark src/poetry/core/_vendor/lark/grammars/lark.lark src/poetry/core/_vendor/lark/grammars/python.lark src/poetry/core/_vendor/lark/grammars/unicode.lark src/poetry/core/_vendor/vendor.txt src/poetry/core/constraints/generic/constraint.py

---

Tips and commands

Interacting with Sourcery

• Trigger a new review: Comment @sourcery-ai review on the pull request.
• Continue discussions: Reply directly to Sourcery's review comments.
• Generate a GitHub issue from a review comment: Ask Sourcery to create an
  issue from a review comment by replying to it. You can also reply to a
  review comment with @sourcery-ai issue to create an issue from it.
• Generate a pull request title: Write @sourcery-ai anywhere in the pull
  request title to generate a title at any time. You can also comment
  @sourcery-ai title on the pull request to (re-)generate the title at any time.
• Generate a pull request summary: Write @sourcery-ai summary anywhere in
  the pull request body to generate a PR summary at any time exactly where you
  want it. You can also comment @sourcery-ai summary on the pull request to
  (re-)generate the summary at any time.
• Generate reviewer's guide: Comment @sourcery-ai guide on the pull
  request to (re-)generate the reviewer's guide at any time.
• Resolve all Sourcery comments: Comment @sourcery-ai resolve on the
  pull request to resolve all Sourcery comments. Useful if you've already
  addressed all the comments and don't want to see them anymore.
• Dismiss all Sourcery reviews: Comment @sourcery-ai dismiss on the pull
  request to dismiss all existing Sourcery reviews. Especially useful if you
  want to start fresh with a new review - don't forget to comment
  @sourcery-ai review to trigger a new review!

Customizing Your Experience

Access your dashboard to:

• Enable or disable review features such as the Sourcery-generated pull request
  summary, the reviewer's guide, and others.
• Change the review language.
• Add, remove or edit custom review instructions.
• Adjust other review settings.

Getting Help

• Contact our support team for questions or feedback.
• Visit our documentation for detailed guides and information.
• Keep in touch with the Sourcery team by following us on X/Twitter, LinkedIn or GitHub.

[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• In constraint_regions you switched from zip(edges, edges[1:]) to pairwise(edges) but there’s no corresponding import change in the diff—either add from itertools import pairwise or qualify it as itertools.pairwise to avoid a NameError.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `constraint_regions` you switched from `zip(edges, edges[1:])` to `pairwise(edges)` but there’s no corresponding import change in the diff—either add `from itertools import pairwise` or qualify it as `itertools.pairwise` to avoid a `NameError`.

## Individual Comments

### Comment 1
<location> `pyproject.toml:64-68` </location>
<code_context>
 fix = true
 line-length = 88
 src = ["src"]
-target-version = "py39"

 [tool.ruff.lint]
</code_context>

<issue_to_address>
**suggestion:** Ruff target-version could be updated to `py310` rather than removed for consistent linting across environments.

Because `requires-python = ">=3.10, <4.0"` is set, dropping `target-version` makes Ruff depend on the local runtime/tooling to infer the version, which can differ between environments. Keeping `target-version = "py310"` makes the applied lint rules (syntax support, built-ins, etc.) deterministic everywhere Ruff runs.

```suggestion
fix = true
line-length = 88
src = ["src"]
target-version = "py310"

[tool.ruff.lint]
```
</issue_to_address>

---

Sourcery is free for open source - if you like our reviews please consider sharing them ✨

• X
• Mastodon
• LinkedIn
• Facebook

_{Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.}