Merge branch 'master' into add-docstring-all-permutations

Author: cclauss

.devcontainer/devcontainer.json

@@ -1,17 +1,25 @@
 {
 	"name": "Python 3",
-	"build": {
-		"dockerfile": "Dockerfile",
-		"context": "..",
-		"args": {
-			// Update 'VARIANT' to pick a Python version: 3, 3.11, 3.10, 3.9, 3.8
-			// Append -bullseye or -buster to pin to an OS version.
-			// Use -bullseye variants on local on arm64/Apple Silicon.
-			"VARIANT": "3.13-bookworm"
-		}
-	},
 
-	"postCreateCommand": "zsh .devcontainer/post_install",
+	// Use a prebuilt dev container image instead of building from a local
+	// Dockerfile. The repo migrated its dependencies to pyproject.toml, so the
+	// old Dockerfile's `COPY requirements.txt` step no longer had a file to copy
+	// and the image build failed. The upstream images already ship Python + a
+	// full toolchain, so pulling one is both faster and less to maintain.
+	//
+	// This repo tracks the latest-and-greatest CPython on the newest stable
+	// Debian. Images are published per CPython minor version on Debian 13
+	// "Trixie" (3.11-trixie ... 3.14-trixie); bump this to the newest available
+	// when a new stable CPython ships.
+	// NOTE: these images do not publish free-threaded (`t`) variants, so 3.14t
+	// cannot be selected via the tag alone -- but the repo's `.python-version`
+	// pins 3.14t, and `uv run`/`uv sync` in the container honor it, so uv gives
+	// contributors free-threaded 3.14t regardless of the base tag.
+	"image": "mcr.microsoft.com/devcontainers/python:latest",
+
+	// Install the tools post_install and CI expect (pre-commit + ruff), plus uv
+	// for the free-threaded workflow above, then run the existing setup script.
+	"postCreateCommand": "pipx install pre-commit ruff uv && zsh .devcontainer/post_install",
 
 	// Configure tool-specific properties.
 	"customizations": {
@@ -20,26 +28,30 @@
 			// Set *default* container specific settings.json values on container create.
 			"settings": {
 				"python.defaultInterpreterPath": "/usr/local/bin/python",
-				"python.linting.enabled": true,
-				"python.formatting.blackPath": "/usr/local/py-utils/bin/black",
-				"python.linting.mypyPath": "/usr/local/py-utils/bin/mypy",
+				// Formatting/linting is handled by Ruff (matches pre-commit and CI).
+				"editor.formatOnSave": true,
+				"[python]": {
+					"editor.defaultFormatter": "charliermarsh.ruff",
+					"editor.codeActionsOnSave": {
+						"source.fixAll": "explicit",
+						"source.organizeImports": "explicit"
+					}
+				},
 				"terminal.integrated.defaultProfile.linux": "zsh"
 			},
 
 			// Add the IDs of extensions you want installed when the container is created.
 			"extensions": [
 				"ms-python.python",
-				"ms-python.vscode-pylance"
+				"ms-python.vscode-pylance",
+				"charliermarsh.ruff"
 			]
 		}
 	},
 
 	// Use 'forwardPorts' to make a list of ports inside the container available locally.
 	// "forwardPorts": [],
 
-	// Use 'postCreateCommand' to run commands after the container is created.
-	// "postCreateCommand": "pip3 install --user -r requirements.txt",
-
 	// Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
 	"remoteUser": "vscode"
 }

.github/skills/code-review/SKILL.md

@@ -0,0 +1,95 @@
+# Skill: Code review for TheAlgorithms/Python
+
+Review a pull request against the rules already written in
+[`CONTRIBUTING.md`](../../../CONTRIBUTING.md). The goal is a review that any
+reviewer (human or AI) can run the same way every time, and that produces a clear,
+kind, actionable verdict.
+
+## How to run this skill
+
+Read the PR diff, then work through the four `CONTRIBUTING.md` sections in order
+and emit the fixed output shape below. Cite the exact rule you are applying and
+suggest the fix — never just "rejected".
+
+### 1. Before contributing / Is this an algorithm?
+
+- [ ] The change adds, fixes, or documents **one algorithm** — not multiple, and
+      not both code and doctest changes in the same PR.
+- [ ] It is a genuine algorithm or data structure (see the *What is an Algorithm?*
+      section), not a script, snippet, how-to-use for an existing API, or exercise
+      dump.
+- [ ] It is **not already in the repository** (search the existing directories).
+- [ ] **No earlier open PR** already does the same thing — link it if one exists.
+- [ ] Properly attributed — no plagiarism; prior sources credited.
+
+### 2. Coding Style
+
+- [ ] `from __future__ import annotations` is not needed because this repo only uses
+      the latest version of CPython.
+- [ ] File and directory names are lowercase, use underscores, and land inside an
+      existing directory.
+- [ ] Public functions/classes have **type hints**.
+- [ ] Public functions have **doctests that actually pass**.
+- [ ] Descriptive variable and function names (no single letters where a word helps).
+- [ ] Code is formatted and lint-clean (`ruff`, `pre-commit`).
+
+> **Optional hint:** When a PR hand-writes a simple class that is mostly a
+> bundle of fields (a manual `__init__` plus `__repr__`/`__eq__`), it is worth
+> **suggesting** `from typing import NamedTuple` or
+> `from dataclasses import dataclass` where they would simplify the code. These
+> are underutilized tools that our contributors would benefit from using where
+> they make sense. Offer it as an optional improvement, not a blocker — do not
+> request changes solely because a class was written the longhand way.
+
+#### When a PR fails `ruff check`
+
+Don't just report the failure — try the mechanical fixes and recommend the one
+that works, in this order:
+
+1. Run `ruff check --fix file_path.py`. If that makes the file pass, recommend
+   that solution — these are the fixes `ruff` considers **safe**.
+2. If it still fails, run `ruff check --fix --unsafe-fixes file_path.py`. If that
+   makes the file pass **and** the resulting diff is genuinely safe (it preserves
+   behavior — review it, don't trust it blindly), recommend that solution and note
+   that it required `--unsafe-fixes`.
+3. If neither passes, or the unsafe fix would change behavior, describe the
+   remaining rule violations and the manual change the author needs to make.
+
+Always quote the exact rule code(s) `ruff` reports (e.g., `ruff rule UP047`,
+`ruff rule RUF100`) so the author can run those commands to read the rules being
+flagged. Also, paste the concrete command you ran.
+
+### 3. Other Requirements for Submissions
+
+- [ ] At least one **Wikipedia (or equivalent) URL** documenting the algorithm.
+- [ ] Docstring explains what the function does and its parameters/returns.
+- [ ] No unnecessary third-party dependencies.
+
+### 4. Verdict — fixed output shape
+
+Emit exactly these headings so reviews are comparable and easy to automate:
+
+```
+### Is this an algorithm? — <yes/no + one-line why>
+### Duplicate / prior-art check — <#NNNN | none found>
+### Coding style — <pass | issues: …>
+### Other requirements (doctests, type hints, descriptive names, Wikipedia URL) — <pass | issues: …>
+### Verdict — <approve | request changes | close> + one-line reason
+```
+
+## Tone
+
+Be specific and kind. Point at the exact `CONTRIBUTING.md` rule and offer the fix
+rather than a bare rejection — first-time and Hacktoberfest contributors are more
+likely to come back and improve the PR when the path forward is clear.
+
+## Map findings to labels
+
+Where a finding matches an existing label, name it so the review lines up with the
+maintenance/cleanup tooling:
+
+- missing/failing doctests → `require tests`
+- missing type hints → `require type hints`
+- non-descriptive names → `require descriptive names`
+- CI red → `tests are failing`
+- otherwise ready for a maintainer → `awaiting reviews`

.github/skills/new-pull-request/SKILL.md

@@ -0,0 +1,57 @@
+# Skill: New pull request for TheAlgorithms/Python
+
+Create a new pull request using the rules already written in
+[`CONTRIBUTING.md`](../../../CONTRIBUTING.md). The goal is that creating a new
+pull request (human or AI) can run the same way every time, and that produces a
+clear, kind, tested, type-hinted, mergeable contribution.
+
+## How to run this skill
+
+Make sure that the local `master` branch is synced with `upstream/master` before
+creating a new pull request.
+
+Create a new clearly named branch for the pull request.  Pull request changes must
+not be made or submitted on the `master` branch.
+
+Never hand-edit or revert the `uv.lock` file. If you add a legitimate
+dependency, let the `uv-lock` pre-commit hook regenerate it — do not touch it by
+hand. A hand-modified `uv.lock` makes the `algorithms-keeper` bot close the pull
+request as invalid, and even a repo maintainer cannot undo that.
+
+Always check at least one Markdown checkbox in the pull request description (the "Describe your change" section), or the
+`algorithms-keeper` bot will close the pull request as invalid.  Any repo maintainer can undo this if you @mention them on the closed pull request.
+
+### 1. Before contributing / Is this an algorithm?
+
+- [ ] The change adds, fixes, or documents **one algorithm** — not multiple, and
+      not both code and doctest changes in the same PR.
+- [ ] It is a genuine algorithm or data structure (see the *What is an Algorithm?*
+      section), not a script, snippet, how-to-use for an existing API, or exercise
+      dump.
+- [ ] It is **not already in the repository** (search the existing directories).
+- [ ] **No earlier open PR** already does the same thing — link it if one exists.
+- [ ] Properly attributed — no plagiarism; prior sources credited.
+
+### 2. Coding Style
+
+- [ ] `from __future__ import annotations` is not needed because this repo only uses
+      the latest version of CPython.
+- [ ] File and directory names are lowercase, use underscores, and land inside an
+      existing directory.
+- [ ] Public functions/classes have **type hints**.
+- [ ] Public functions have **doctests that actually pass**.
+- [ ] Descriptive variable and function names (no single letters where a word helps).
+- [ ] For a simple class that is mostly a bundle of fields, **consider**
+      `from typing import NamedTuple` or `from dataclasses import dataclass`
+      instead of a hand-written `__init__`/`__repr__`/`__eq__`. These are
+      underutilized tools that make simple classes shorter and clearer — use
+      them where they genuinely simplify the code, not everywhere.
+- [ ] Code is formatted and lint-clean (`ruff`, `pre-commit`).
+- [ ] `DIRECTORY.md` and `README.md` are **not hand-edited** — the
+      `algorithms-keeper` bot regenerates them automatically after merge.
+
+### 3. Other Requirements for Submissions
+
+- [ ] At least one **Wikipedia (or equivalent) URL** documenting the algorithm.
+- [ ] Docstring explains what the function does and its parameters/returns.
+- [ ] No unnecessary third-party dependencies.

.github/workflows/build.yml

@@ -9,25 +9,38 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - run: sudo apt-get update && sudo apt-get install -y libhdf5-dev
       - uses: actions/checkout@v7
       - uses: astral-sh/setup-uv@v7
         with:
           enable-cache: true
           cache-dependency-glob: uv.lock
       - uses: actions/setup-python@v7
         with:
-          python-version: 3.14
+          python-version-file: .python-version
           allow-prereleases: true
       - run: uv sync --group=test
       - name: Run tests
-        # TODO: #8818 Re-enable quantum tests
+        # opencv-python is gated out on 3.14t (no cp314t wheel yet), so skip the
+        # files that import cv2. Pure-Python algorithms in computer_vision/ and
+        # data_compression/ still run; digital_image_processing/ is almost entirely
+        # cv2-based so it is skipped as a tree. Re-enable when a cp314t wheel ships.
+        # --ignore-gil-enabled: some compiled deps (sklearn, xgboost, ...) don't
+        # yet ship the Py_mod_gil slot, so importing them re-enables the GIL under
+        # 3.14t. That's an upstream-wheel gap, not our code; the flag lets the suite
+        # run anyway and pytest-run-parallel still reports which tests are not
+        # thread-safe. Drop the flag once the scientific stack ships free-threaded wheels.
+        # qiskit is likewise gated out of the 3.14t deps (Qiskit/qiskit#16893), so the
+        # single file that imports it (quantum/q_fourier_transform.py) is skipped too.
         run: uv run --with=pytest-run-parallel pytest
-          --iterations=8 --parallel-threads=auto
+          --iterations=8 --parallel-threads=auto --ignore-gil-enabled
           --ignore=computer_vision/cnn_classification.py
+          --ignore=computer_vision/flip_augmentation.py
+          --ignore=computer_vision/harris_corner.py
+          --ignore=computer_vision/mosaic_augmentation.py
+          --ignore=data_compression/peak_signal_to_noise_ratio.py
+          --ignore=digital_image_processing/
           --ignore=docs/conf.py
           --ignore=dynamic_programming/k_means_clustering_tensorflow.py
-          --ignore=machine_learning/local_weighted_learning/local_weighted_learning.py
           --ignore=machine_learning/lstm/lstm_prediction.py
           --ignore=neural_network/input_data.py
           --ignore=project_euler/

.github/workflows/devcontainer_ci.yml

@@ -4,9 +4,11 @@ on:
   push:
     paths:
       - ".devcontainer/**"
+      - ".github/workflows/devcontainer_ci.yml"
   pull_request:
     paths:
       - ".devcontainer/**"
+      - ".github/workflows/devcontainer_ci.yml"
 
 jobs:
   build:

.github/workflows/directory_writer.yml

@@ -11,7 +11,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-python@v7
         with:
-          python-version: 3.14
+          python-version-file: .python-version
           allow-prereleases: true
       - name: Write DIRECTORY.md
         run: |

.github/workflows/hacktoberfest_prep.yml

@@ -0,0 +1,69 @@
+# Daily refresh of the Hacktoberfest 2026 open-PR cleanup tracker.
+# Ticks off any tracked pull request that has since been merged/closed, and
+# rewrites the "Automated statistics" section (open issue/PR counts + the top
+# three `awaiting reviews` directories). The job fails on purpose once
+# Hacktoberfest 2026 has begun (>= 2026-10-01), which is the signal to retire it.
+name: hacktoberfest_prep
+
+on:
+  push:
+    paths:
+      - ".github/workflows/hacktoberfest_prep.yml"
+      - "scripts/hacktoberfest_prep_update.py"
+  pull_request:
+    paths:
+      - ".github/workflows/hacktoberfest_prep.yml"
+      - "scripts/hacktoberfest_prep_update.py"
+  schedule:
+    - cron: "50 11 * * *" # 11:50 UTC every day
+  workflow_dispatch: # allow a manual run while testing
+
+permissions:
+  contents: write
+
+jobs:
+  hacktoberfest-prep:
+    # No point running on forks — this pushes to the repo's own docs file.
+    if: github.repository == 'TheAlgorithms/Python'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: actions/setup-python@v7
+        with:
+          python-version-file: .python-version
+          allow-prereleases: true
+      - name: Install dependencies
+        run: python -m pip install --upgrade "httpx2>=2.0.1"
+      - name: Update the tracker
+        id: update
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_REPOSITORY: ${{ github.repository }}
+        # Don't let the intentional post-Oct-1 failure stop the commit step;
+        # capture the exit code and re-raise it after pushing any changes.
+        run: |
+          set +e
+          python scripts/hacktoberfest_prep_update.py
+          echo "exit_code=$?" >> "$GITHUB_OUTPUT"
+      # Dry run on push / pull_request: show the diff the script produced but
+      # do NOT commit or push. This lets a PR prove the tracker still gathers
+      # its data and rewrites docs/hacktober_2026_prep.md correctly without
+      # leaving a permanent commit. Only the schedule/manual runs persist.
+      - name: Show changes (dry run)
+        if: github.event_name == 'push' || github.event_name == 'pull_request'
+        run: |
+          echo "Dry run (${{ github.event_name }}): showing git diff, not committing."
+          git --no-pager diff -- docs/hacktober_2026_prep.md
+          if git diff --quiet -- docs/hacktober_2026_prep.md; then
+            echo "No changes to docs/hacktober_2026_prep.md."
+          fi
+      - name: Commit any changes
+        if: github.event_name != 'push' && github.event_name != 'pull_request'
+        run: |
+          git config --global user.name "$GITHUB_ACTOR"
+          git config --global user.email "$GITHUB_ACTOR@users.noreply.github.com"
+          git add docs/hacktober_2026_prep.md
+          git commit -m "chore: refresh Hacktoberfest 2026 prep tracker" || echo "No changes to commit"
+          git push || echo "Nothing to push"
+      - name: Propagate the script's exit code
+        run: exit ${{ steps.update.outputs.exit_code }}