feat(pyproject): release v1.7.0 — Python pyproject.toml version bump

Add internal/pyproject package with ReadVersion and WriteVersion for
pyproject.toml files. Reads [project].version (PEP 621) first, then
falls back to [tool.poetry].version. Section boundaries are detected
via TOML's rule that headers always start at the beginning of a line
(\n[ pattern), so inline arrays with [ characters don't interfere.

Config follows the established multi-value pattern:
- python.pyproject_toml: single path (opt-in, no default)
- python.pyproject_tomls: list for monorepos (overrides single)
- --pyproject flag overrides pyproject_toml and clears pyproject_tomls

100% per-package statement coverage maintained across all 14 packages;
FuzzReadVersion and FuzzWriteVersion added per fuzzing guidelines.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.releaser.yml

@@ -50,6 +50,16 @@ git:
   #   - "packages/frontend/package.json"
   #   - "packages/backend/package.json"
 
+# python:
+  # Single pyproject.toml path (opt-in — no default).
+  # Reads [project].version (PEP 621) first, then [tool.poetry].version.
+  # pyproject_toml: "pyproject.toml"
+
+  # Multiple pyproject.toml paths for monorepos (overrides pyproject_toml).
+  # pyproject_tomls:
+  #   - "pyproject.toml"
+  #   - "packages/cli/pyproject.toml"
+
 # gradle:
   # Single build.gradle or build.gradle.kts path (opt-in — no default).
   # Both Groovy DSL (single-quoted) and Kotlin DSL (double-quoted) are supported.

CHANGELOG.md

@@ -3,6 +3,15 @@
 All notable changes to this project will be documented in this file.
 Format: [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
+## [1.7.0] - 2026-07-12
+
+### Added
+
+- **Python `pyproject.toml` support** — new `internal/pyproject` package; reads `[project].version` (PEP 621) first, then `[tool.poetry].version` (Poetry); original formatting preserved on write; `regexp.QuoteMeta` ensures safety with dot-containing version strings
+- **`python.pyproject_toml` / `python.pyproject_tomls` config** — opt-in, no default; `pyproject_tomls` list overrides `pyproject_toml` for monorepos; follows the established multi-value pattern (Maven, Node, Gradle)
+- **`--pyproject <path>` flag** — overrides `python.pyproject_toml` and clears `pyproject_tomls`; shown in verbose config table as `python.paths`
+- **`FuzzReadVersion` / `FuzzWriteVersion`** in `internal/pyproject` — 100% per-package statement coverage maintained across all 14 packages
+
 ## [1.6.3] - 2026-07-11
 
 ### Added

CLAUDE.md

@@ -62,6 +62,7 @@ All seed cases must pass. The table below is authoritative — keep it in sync w
 | `internal/changelog` | `FuzzUpdate` | rewrites arbitrary existing file content |
 | `internal/commits` | `FuzzParse` | parses arbitrary commit message strings |
 | `internal/gradle` | `FuzzReadVersion`, `FuzzWriteVersion` | reads/rewrites arbitrary Gradle build file content |
+| `internal/pyproject` | `FuzzReadVersion`, `FuzzWriteVersion` | reads/rewrites arbitrary pyproject.toml content |
 | `internal/glclient` | `FuzzEncodeProjectPath` | encodes arbitrary project path strings |
 | `internal/maven` | `FuzzReadVersion`, `FuzzReplaceProjectVersion` | reads/rewrites arbitrary XML file content |
 | `internal/node` | `FuzzReadVersion`, `FuzzWriteVersion` | reads/rewrites arbitrary JSON file content |

README.md

@@ -2,7 +2,7 @@
 
 <img src="docs/static/images/releaser-logo-128.png" alt="releaser logo" width="128">
 
-![release](https://img.shields.io/badge/release-v1.6.3-blue.svg)
+![release](https://img.shields.io/badge/release-v1.7.0-blue.svg)
 
 A CI-friendly release automation tool for GitFlow workflows using Conventional Commits.
 
@@ -125,6 +125,12 @@ gradle:                                              # opt-in — no default; om
   #   - "build.gradle"
   #   - "module-a/build.gradle"
 
+python:                                              # opt-in — no default; omit to skip
+  # pyproject_toml: "pyproject.toml"                 # PEP 621 [project] or [tool.poetry]
+  # pyproject_tomls:                                 # monorepo: list overrides pyproject_toml
+  #   - "pyproject.toml"
+  #   - "packages/cli/pyproject.toml"
+
 gitlab:
   url: "https://gitlab.example.com"                  # or env CI_SERVER_URL
   token: ""                                          # env GITLAB_TOKEN (never commit this)

ROADMAP.md

@@ -86,5 +86,5 @@
 ## Future / backlog
 
 - ~~Gradle support (`build.gradle` / `build.gradle.kts`)~~ — ✓ shipped v1.6.0 (`internal/gradle`; Groovy + Kotlin DSL; multi-module via `gradle.build_files`; `--gradle` flag)
-- Python `pyproject.toml` version bump (`[project].version` and `[tool.poetry].version`; single and multi-path like Maven's `pom_paths`)
+- ~~Python `pyproject.toml` version bump (`[project].version` and `[tool.poetry].version`; single and multi-path like Maven's `pom_paths`)~~ — ✓ shipped v1.7.0 (`internal/pyproject`; PEP 621 + Poetry; `python.pyproject_tomls`; `--pyproject` flag)
 - Slack / Teams notification on release

cmd/main.go

@@ -20,6 +20,7 @@ import (
 	"git.k3nny.fr/releaser/internal/glclient"
 	"git.k3nny.fr/releaser/internal/gradle"
 	"git.k3nny.fr/releaser/internal/maven"
+	"git.k3nny.fr/releaser/internal/pyproject"
 	"git.k3nny.fr/releaser/internal/node"
 	"git.k3nny.fr/releaser/internal/notes"
 	semver "git.k3nny.fr/releaser/internal/version"
@@ -90,6 +91,17 @@ gradle:
   #   - "module-a/build.gradle"
   #   - "module-b/build.gradle"
 
+python:
+  # Single pyproject.toml path (opt-in — no default).
+  # Reads [project].version (PEP 621) first, then [tool.poetry].version.
+  # pyproject_toml: "pyproject.toml"
+
+  # Multiple pyproject.toml paths for monorepos (overrides pyproject_toml).
+  # pyproject_tomls:
+  #   - "pyproject.toml"
+  #   - "packages/cli/pyproject.toml"
+  #   - "packages/lib/pyproject.toml"
+
 gitlab:
   # GitLab instance URL. Falls back to the CI_SERVER_URL environment variable.
   # url: "https://gitlab.example.com"
@@ -161,8 +173,9 @@ func newRootCmd() *cobra.Command {
 		branchOverride  string
 		repoPath        string
 		pomOverride     string
-		gradleOverride  string
+		gradleOverride     string
-		changelogFile   string
+		pyprojectOverride  string
+		changelogFile      string
 		tagPrefixFlag   string
 		tagPrefixSet    bool
 		patternFlag     string
@@ -184,8 +197,9 @@ func newRootCmd() *cobra.Command {
 				repoPath:       repoPath,
 				branchOverride: branchOverride,
 				pomOverride:    pomOverride,
-				gradleOverride: gradleOverride,
+				gradleOverride:    gradleOverride,
-				changelogFile:  changelogFile,
+				pyprojectOverride: pyprojectOverride,
+				changelogFile:     changelogFile,
 				tagPrefixFlag:  tagPrefixFlag,
 				tagPrefixSet:   tagPrefixSet,
 				patternFlag:    patternFlag,
@@ -211,6 +225,7 @@ func newRootCmd() *cobra.Command {
 	root.Flags().StringVar(&repoPath, "repo", ".", "path to git repository")
 	root.Flags().StringVar(&pomOverride, "pom", "", "override maven.pom_path from config")
 	root.Flags().StringVar(&gradleOverride, "gradle", "", "override gradle.build_file from config")
+	root.Flags().StringVar(&pyprojectOverride, "pyproject", "", "override python.pyproject_toml from config")
 	root.Flags().StringVar(&changelogFile, "changelog-file", "CHANGELOG.md", "path to changelog file relative to repo root")
 	root.Flags().StringVar(&tagPrefixFlag, "tag-prefix", "", "override git.tag_prefix from config")
 	root.Flags().StringVar(&patternFlag, "branch-pattern", "", "override git.branch_pattern from config")
@@ -235,9 +250,10 @@ type options struct {
 	repoPath        string
 	branchOverride  string
 	pomOverride     string
-	gradleOverride  string
+	gradleOverride    string
-	changelogFile   string
+	pyprojectOverride string
-	tagPrefixFlag   string
+	changelogFile     string
+	tagPrefixFlag     string
 	tagPrefixSet    bool
 	patternFlag     string
 	patternSet      bool
@@ -296,6 +312,13 @@ func printVerboseConfig(cfg config.Config, src config.Sources) {
 			}
 			return strings.Join(paths, ", ")
 		}()},
+		{"python.paths", func() string {
+			paths := cfg.Python.EffectivePaths()
+			if len(paths) == 0 {
+				return "(not configured)"
+			}
+			return strings.Join(paths, ", ")
+		}()},
 		{"gitlab.url", cfg.GitLab.URL},
 		{"gitlab.token", func() string {
 			if cfg.GitLab.Token != "" {
@@ -388,6 +411,11 @@ func run(o options) error {
 		cfg.Gradle.BuildFiles = nil
 		src["gradle.build_files"] = "flag: --gradle"
 	}
+	if o.pyprojectOverride != "" {
+		cfg.Python.PyprojectTOML = o.pyprojectOverride
+		cfg.Python.PyprojectTOMLs = nil
+		src["python.pyproject_tomls"] = "flag: --pyproject"
+	}
 	if o.patternSet {
 		cfg.Git.BranchPattern = o.patternFlag
 		src["git.branch_pattern"] = "flag: --branch-pattern"
@@ -594,6 +622,20 @@ func run(o options) error {
 			filesToCommit = append(filesToCommit, relGradlePath)
 		}
 
+		// pyproject.toml (opt-in via python.pyproject_toml / python.pyproject_tomls)
+		for _, relPyprojectPath := range cfg.Python.EffectivePaths() {
+			pyprojectPath := filepath.Join(absRepo, relPyprojectPath)
+			currentPyVersion, err := pyproject.ReadVersion(pyprojectPath)
+			if err != nil {
+				return fmt.Errorf("read pyproject version: %w", err)
+			}
+			if err := pyproject.WriteVersion(pyprojectPath, currentPyVersion, nextVersion); err != nil {
+				return fmt.Errorf("update pyproject version: %w", err)
+			}
+			logDone("%s: %s → %s", relPyprojectPath, currentPyVersion, nextVersion)
+			filesToCommit = append(filesToCommit, relPyprojectPath)
+		}
+
 		// CHANGELOG.md
 		changelogAbsPath := filepath.Join(absRepo, o.changelogFile)
 		if err := changelog.Update(changelogAbsPath, nextTag, nextVersion, messages); err != nil {

cmd/main_test.go

@@ -1101,6 +1101,7 @@ func TestPrintVerboseConfigBumpRulesAndNode(t *testing.T) {
 		},
 		Node:   config.NodeConfig{PackageJSON: "package.json"},
 		Gradle: config.GradleConfig{BuildFile: "build.gradle"},
+		Python: config.PythonConfig{PyprojectTOML: "pyproject.toml"},
 	}
 	src := config.Sources{}
 
@@ -1122,6 +1123,9 @@ func TestPrintVerboseConfigBumpRulesAndNode(t *testing.T) {
 	if !strings.Contains(output, "build.gradle") {
 		t.Error("expected 'build.gradle' in output for gradle.paths")
 	}
+	if !strings.Contains(output, "pyproject.toml") {
+		t.Error("expected 'pyproject.toml' in output for python.paths")
+	}
 }
 
 // ── node package.json handling ────────────────────────────────────────────────
@@ -1321,3 +1325,143 @@ func TestRunGradleWriteVersionFails(t *testing.T) {
 		t.Fatal("expected error when build.gradle is read-only")
 	}
 }
+
+// ── pyproject.toml handling ───────────────────────────────────────────────────
+
+func writePyprojectFile(t *testing.T, dir, ver string) {
+	t.Helper()
+	content := fmt.Sprintf("[project]\nname = \"my-app\"\nversion = \"%s\"\n", ver)
+	if err := os.WriteFile(filepath.Join(dir, "pyproject.toml"), []byte(content), 0644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestRunPyprojectVersionBump(t *testing.T) {
+	dir := t.TempDir()
+	repo, err := gogit.PlainInit(dir, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	writePyprojectFile(t, dir, "0.0.0")
+	commitAll(t, repo, dir, "chore: init")
+
+	os.WriteFile(filepath.Join(dir, ".releaser.yml"), []byte("python:\n  pyproject_toml: \"pyproject.toml\"\n"), 0644)
+
+	addFile(t, dir, "x.go", "// fix")
+	w, _ := repo.Worktree()
+	w.Add("x.go")
+	w.Commit("fix: something", &gogit.CommitOptions{Author: testSig()})
+
+	if err := execCmd(t, "--no-push", "--branch", "release/1.2", "--repo", dir); err != nil {
+		t.Fatalf("pyproject version bump: unexpected error: %v", err)
+	}
+
+	data, _ := os.ReadFile(filepath.Join(dir, "pyproject.toml"))
+	if !strings.Contains(string(data), `version = "1.2.0"`) {
+		t.Errorf("expected version 1.2.0 in pyproject.toml, got: %s", data)
+	}
+}
+
+func TestRunPyprojectPoetryVersionBump(t *testing.T) {
+	dir := t.TempDir()
+	repo, err := gogit.PlainInit(dir, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	content := "[tool.poetry]\nname = \"my-app\"\nversion = \"0.0.0\"\n"
+	os.WriteFile(filepath.Join(dir, "pyproject.toml"), []byte(content), 0644)
+	commitAll(t, repo, dir, "chore: init")
+
+	os.WriteFile(filepath.Join(dir, ".releaser.yml"), []byte("python:\n  pyproject_toml: \"pyproject.toml\"\n"), 0644)
+
+	addFile(t, dir, "x.go", "// fix")
+	w, _ := repo.Worktree()
+	w.Add("x.go")
+	w.Commit("fix: something", &gogit.CommitOptions{Author: testSig()})
+
+	if err := execCmd(t, "--no-push", "--branch", "release/1.2", "--repo", dir); err != nil {
+		t.Fatalf("poetry version bump: unexpected error: %v", err)
+	}
+
+	data, _ := os.ReadFile(filepath.Join(dir, "pyproject.toml"))
+	if !strings.Contains(string(data), `version = "1.2.0"`) {
+		t.Errorf("expected version 1.2.0 in pyproject.toml, got: %s", data)
+	}
+}
+
+func TestRunPyprojectOverrideFlag(t *testing.T) {
+	dir := t.TempDir()
+	repo, err := gogit.PlainInit(dir, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.MkdirAll(filepath.Join(dir, "sub"), 0755); err != nil {
+		t.Fatal(err)
+	}
+	content := "[project]\nversion = \"0.0.0\"\n"
+	os.WriteFile(filepath.Join(dir, "sub", "pyproject.toml"), []byte(content), 0644)
+	commitAll(t, repo, dir, "chore: init")
+
+	addFile(t, dir, "x.go", "// fix")
+	w, _ := repo.Worktree()
+	w.Add("x.go")
+	w.Commit("fix: something", &gogit.CommitOptions{Author: testSig()})
+
+	if err := execCmd(t, "--no-push", "--branch", "release/1.2", "--repo", dir, "--pyproject", "sub/pyproject.toml"); err != nil {
+		t.Fatalf("--pyproject flag: unexpected error: %v", err)
+	}
+
+	data, _ := os.ReadFile(filepath.Join(dir, "sub", "pyproject.toml"))
+	if !strings.Contains(string(data), `version = "1.2.0"`) {
+		t.Errorf("expected version 1.2.0, got: %s", data)
+	}
+}
+
+func TestRunPyprojectReadVersionFails(t *testing.T) {
+	dir := t.TempDir()
+	repo, err := gogit.PlainInit(dir, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// pyproject.toml with no version field
+	os.WriteFile(filepath.Join(dir, "pyproject.toml"), []byte("[build-system]\nrequires=[]\n"), 0644)
+	commitAll(t, repo, dir, "chore: init")
+
+	os.WriteFile(filepath.Join(dir, ".releaser.yml"), []byte("python:\n  pyproject_toml: \"pyproject.toml\"\n"), 0644)
+
+	addFile(t, dir, "x.go", "// fix")
+	w, _ := repo.Worktree()
+	w.Add("x.go")
+	w.Commit("fix: something", &gogit.CommitOptions{Author: testSig()})
+
+	if err := execCmd(t, "--branch", "release/1.2", "--repo", dir); err == nil {
+		t.Fatal("expected error when pyproject.toml has no version")
+	}
+}
+
+func TestRunPyprojectWriteVersionFails(t *testing.T) {
+	if os.Getuid() == 0 {
+		t.Skip("skipping: chmod restrictions do not apply when running as root")
+	}
+	dir := t.TempDir()
+	repo, err := gogit.PlainInit(dir, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	writePyprojectFile(t, dir, "0.0.0")
+	commitAll(t, repo, dir, "chore: init")
+
+	os.WriteFile(filepath.Join(dir, ".releaser.yml"), []byte("python:\n  pyproject_toml: \"pyproject.toml\"\n"), 0644)
+
+	addFile(t, dir, "x.go", "// fix")
+	w, _ := repo.Worktree()
+	w.Add("x.go")
+	w.Commit("fix: something", &gogit.CommitOptions{Author: testSig()})
+
+	os.Chmod(filepath.Join(dir, "pyproject.toml"), 0444)
+	defer os.Chmod(filepath.Join(dir, "pyproject.toml"), 0644)
+
+	if err := execCmd(t, "--branch", "release/1.2", "--repo", dir); err == nil {
+		t.Fatal("expected error when pyproject.toml is read-only")
+	}
+}

docs/content/changelog.md

@@ -3,6 +3,12 @@ title: Changelog
 weight: 50
 ---
 
+## v1.7.0 — 2026-07-12
+
+### Added
+
+- **Python `pyproject.toml` support** — opt-in via `python.pyproject_toml` (single) or `python.pyproject_tomls` (list); reads `[project].version` (PEP 621) first, then `[tool.poetry].version`; original formatting preserved; `--pyproject <path>` CLI flag for one-off overrides
+
 ## v1.6.0 — 2026-07-11
 
 ### Added

docs/content/configuration.md

@@ -53,6 +53,14 @@ gradle:                                              # opt-in — omit section t
   #   - "build.gradle"
   #   - "module-a/build.gradle"
 
+python:                                              # opt-in — omit section to skip
+  # pyproject_toml: "pyproject.toml"                 # PEP 621 [project].version or [tool.poetry].version
+
+  # Monorepo: list overrides pyproject_toml.
+  # pyproject_tomls:
+  #   - "pyproject.toml"
+  #   - "packages/cli/pyproject.toml"
+
 gitlab:
   url: "https://gitlab.example.com"                  # or env CI_SERVER_URL
   token: ""                                          # prefer env GITLAB_TOKEN
@@ -128,6 +136,27 @@ node:
     - "packages/backend/package.json"
 ```
 
+## Python support
+
+The `python` section is opt-in — if omitted, no `pyproject.toml` is touched. `releaser` reads `[project].version` (PEP 621) first; if not found it falls back to `[tool.poetry].version`. The original file formatting is preserved on write.
+
+```yaml
+python:
+  pyproject_toml: "pyproject.toml"
+```
+
+Use `pyproject_tomls` for monorepos:
+
+```yaml
+python:
+  pyproject_tomls:
+    - "pyproject.toml"
+    - "packages/cli/pyproject.toml"
+    - "packages/lib/pyproject.toml"
+```
+
+The `--pyproject <path>` CLI flag sets a single path and clears `pyproject_tomls`.
+
 ## Gradle support
 
 The `gradle` section is opt-in — if omitted, no build file is touched. Both Groovy DSL (`version = '1.2.3'`) and Kotlin DSL (`version = "1.2.3"`) are supported; the original quote style is preserved on write.

docs/content/usage.md

@@ -40,6 +40,7 @@ releaser --verbose --dry-run
 | `--tag-prefix <prefix>` | `""` | Prefix for version tags (e.g. `v` → `v1.2.3`) |
 | `--pom <path>` | `pom.xml` | Path to pom.xml relative to repo root |
 | `--gradle <path>` | — | Override `gradle.build_file` from config |
+| `--pyproject <path>` | — | Override `python.pyproject_toml` from config |
 | `--changelog-file <path>` | `CHANGELOG.md` | Path to changelog file |
 | `--release-env-file <path>` | `release.env` | Path for dotenv artifact; pass `""` to disable |
 | `--no-commit` | false | Update version files but stop before committing |

internal/config/config.go

@@ -17,8 +17,9 @@ type Config struct {
 	Git    GitConfig    `yaml:"git"`
 	Maven  MavenConfig  `yaml:"maven"`
 	Node   NodeConfig   `yaml:"node"`
-	Gradle GradleConfig `yaml:"gradle"`
+	Gradle  GradleConfig  `yaml:"gradle"`
-	GitLab GitLabConfig `yaml:"gitlab"`
+	Python  PythonConfig  `yaml:"python"`
+	GitLab  GitLabConfig  `yaml:"gitlab"`
 	GitHub GitHubConfig `yaml:"github"`
 }
 
@@ -91,6 +92,23 @@ func (g GradleConfig) EffectiveBuildFiles() []string {
 	return nil
 }
 
+type PythonConfig struct {
+	PyprojectTOML  string   `yaml:"pyproject_toml"`  // single path (opt-in, no default)
+	PyprojectTOMLs []string `yaml:"pyproject_tomls"` // multiple paths; overrides PyprojectTOML
+}
+
+// EffectivePaths returns the list of pyproject.toml paths to process.
+// Returns nil when no python paths are configured (python processing is opt-in).
+func (p PythonConfig) EffectivePaths() []string {
+	if len(p.PyprojectTOMLs) > 0 {
+		return p.PyprojectTOMLs
+	}
+	if p.PyprojectTOML != "" {
+		return []string{p.PyprojectTOML}
+	}
+	return nil
+}
+
 type GitLabConfig struct {
 	URL     string `yaml:"url"`
 	Token   string `yaml:"token"`
@@ -135,9 +153,11 @@ func defaultSources() Sources {
 		"maven.pom_paths":         "default",
 		"node.package_json":       "default",
 		"node.package_jsons":      "default",
-		"gradle.build_file":       "default",
+		"gradle.build_file":        "default",
-		"gradle.build_files":      "default",
+		"gradle.build_files":       "default",
-		"gitlab.url":              "default",
+		"python.pyproject_toml":    "default",
+		"python.pyproject_tomls":   "default",
+		"gitlab.url":               "default",
 		"gitlab.token":            "default",
 		"gitlab.project":          "default",
 		"github.token":            "default",
@@ -219,6 +239,12 @@ func LoadWithSources(dir string) (Config, Sources, error) {
 	if len(overlay.Gradle.BuildFiles) > 0 {
 		src["gradle.build_files"] = "config file"
 	}
+	if overlay.Python.PyprojectTOML != "" {
+		src["python.pyproject_toml"] = "config file"
+	}
+	if len(overlay.Python.PyprojectTOMLs) > 0 {
+		src["python.pyproject_tomls"] = "config file"
+	}
 	if overlay.GitLab.URL != "" {
 		src["gitlab.url"] = "config file"
 	}

internal/config/config_test.go

@@ -338,6 +338,49 @@ func TestLoadGradleBuildFilesSources(t *testing.T) {
 	}
 }
 
+func TestPythonEffectivePaths(t *testing.T) {
+	if got := (PythonConfig{}).EffectivePaths(); got != nil {
+		t.Errorf("empty config: got %v, want nil", got)
+	}
+	if got := (PythonConfig{PyprojectTOML: "pyproject.toml"}).EffectivePaths(); len(got) != 1 || got[0] != "pyproject.toml" {
+		t.Errorf("single path: got %v", got)
+	}
+	p := PythonConfig{PyprojectTOML: "pyproject.toml", PyprojectTOMLs: []string{"a/pyproject.toml", "b/pyproject.toml"}}
+	if got := p.EffectivePaths(); len(got) != 2 || got[0] != "a/pyproject.toml" {
+		t.Errorf("multi-path priority: got %v", got)
+	}
+}
+
+func TestLoadPythonSources(t *testing.T) {
+	dir := t.TempDir()
+	content := "python:\n  pyproject_toml: \"pyproject.toml\"\n"
+	if err := os.WriteFile(filepath.Join(dir, filename), []byte(content), 0644); err != nil {
+		t.Fatal(err)
+	}
+	_, src, err := LoadWithSources(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if src["python.pyproject_toml"] != "config file" {
+		t.Errorf("src[python.pyproject_toml] = %q, want %q", src["python.pyproject_toml"], "config file")
+	}
+}
+
+func TestLoadPythonPathsSources(t *testing.T) {
+	dir := t.TempDir()
+	content := "python:\n  pyproject_tomls:\n    - \"a/pyproject.toml\"\n    - \"b/pyproject.toml\"\n"
+	if err := os.WriteFile(filepath.Join(dir, filename), []byte(content), 0644); err != nil {
+		t.Fatal(err)
+	}
+	_, src, err := LoadWithSources(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if src["python.pyproject_tomls"] != "config file" {
+		t.Errorf("src[python.pyproject_tomls] = %q, want %q", src["python.pyproject_tomls"], "config file")
+	}
+}
+
 func TestLoadPartialOverride(t *testing.T) {
 	dir := t.TempDir()
 	// Only override tag_prefix — commit_message should keep its default

internal/pyproject/pyproject.go

@@ -0,0 +1,74 @@
+package pyproject
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+)
+
+// sectionRe matches a TOML section from its header to the next header (or end of file).
+// TOML section headers always appear at the start of a line, so \n[ is a reliable boundary.
+var (
+	projectSectionRe = regexp.MustCompile(`(?s)\[project\].*?(?:\n\[|\z)`)
+	poetrySectionRe  = regexp.MustCompile(`(?s)\[tool\.poetry\].*?(?:\n\[|\z)`)
+)
+
+// versionLineRe matches version = "x.y.z" on its own line inside a section.
+var versionLineRe = regexp.MustCompile(`(?m)^version\s*=\s*"([^"]+)"`)
+
+// ReadVersion returns the project version from a pyproject.toml file.
+// It checks [project] (PEP 621) first, then [tool.poetry] (Poetry).
+func ReadVersion(path string) (string, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return "", fmt.Errorf("read %s: %w", path, err)
+	}
+	content := string(data)
+	for _, sectionRe := range []*regexp.Regexp{projectSectionRe, poetrySectionRe} {
+		section := sectionRe.FindString(content)
+		if section == "" {
+			continue
+		}
+		m := versionLineRe.FindStringSubmatch(section)
+		if m != nil {
+			return m[1], nil
+		}
+	}
+	return "", fmt.Errorf("no version found in %s", path)
+}
+
+// WriteVersion replaces the project version in a pyproject.toml file in-place.
+// oldVersion must match what ReadVersion returned.
+func WriteVersion(path, oldVersion, newVersion string) error {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return fmt.Errorf("read %s: %w", path, err)
+	}
+	updated, ok := replaceVersion(string(data), oldVersion, newVersion)
+	if !ok {
+		return fmt.Errorf("version %q not found in %s", oldVersion, path)
+	}
+	return os.WriteFile(path, []byte(updated), 0644)
+}
+
+// replaceVersion finds and replaces the version in the first [project] or [tool.poetry]
+// section that contains it. Returns the updated content and true on success.
+// regexp.QuoteMeta is used so version strings with dots or specials are safe.
+func replaceVersion(content, oldVersion, newVersion string) (string, bool) {
+	re := regexp.MustCompile(`(?m)^(version\s*=\s*)"` + regexp.QuoteMeta(oldVersion) + `"`)
+	for _, sectionRe := range []*regexp.Regexp{projectSectionRe, poetrySectionRe} {
+		loc := sectionRe.FindStringIndex(content)
+		if loc == nil {
+			continue
+		}
+		section := content[loc[0]:loc[1]]
+		m := re.FindStringSubmatchIndex(section)
+		if m == nil {
+			continue
+		}
+		// m[0]:m[1] = full match; m[2]:m[3] = group 1 (prefix "version = ")
+		newSection := section[:m[0]] + section[m[2]:m[3]] + `"` + newVersion + `"` + section[m[1]:]
+		return content[:loc[0]] + newSection + content[loc[1]:], true
+	}
+	return content, false
+}

internal/pyproject/pyproject_test.go

@@ -0,0 +1,232 @@
+package pyproject
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const pyprojectPEP621 = `[project]
+name = "my-package"
+version = "1.2.3"
+description = "A test package"
+dependencies = ["requests>=2.0", "click>=8.0"]
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+`
+
+const pyprojectPoetry = `[tool.poetry]
+name = "my-package"
+version = "1.2.3"
+description = "A test package"
+
+[tool.poetry.dependencies]
+python = "^3.9"
+requests = "^2.0"
+`
+
+const pyprojectBoth = `[project]
+name = "my-package"
+version = "1.2.3"
+
+[tool.poetry]
+name = "my-package"
+version = "1.2.3"
+`
+
+const pyprojectBuildSystemFirst = `[build-system]
+requires = ["hatchling"]
+
+[project]
+name = "my-package"
+version = "1.2.3"
+`
+
+func writePyproject(t *testing.T, content string) string {
+	t.Helper()
+	path := filepath.Join(t.TempDir(), "pyproject.toml")
+	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		t.Fatal(err)
+	}
+	return path
+}
+
+// ── ReadVersion ───────────────────────────────────────────────────────────────
+
+func TestReadVersionPEP621(t *testing.T) {
+	got, err := ReadVersion(writePyproject(t, pyprojectPEP621))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "1.2.3" {
+		t.Errorf("got %q, want 1.2.3", got)
+	}
+}
+
+func TestReadVersionPoetry(t *testing.T) {
+	got, err := ReadVersion(writePyproject(t, pyprojectPoetry))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "1.2.3" {
+		t.Errorf("got %q, want 1.2.3", got)
+	}
+}
+
+func TestReadVersionPEP621TakesPrecedence(t *testing.T) {
+	// When both [project] and [tool.poetry] are present, [project] wins.
+	got, err := ReadVersion(writePyproject(t, pyprojectBoth))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "1.2.3" {
+		t.Errorf("got %q, want 1.2.3", got)
+	}
+}
+
+func TestReadVersionBuildSystemIgnored(t *testing.T) {
+	// version under [build-system] must not be returned.
+	got, err := ReadVersion(writePyproject(t, pyprojectBuildSystemFirst))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "1.2.3" {
+		t.Errorf("got %q, want 1.2.3", got)
+	}
+}
+
+func TestReadVersionMissingFile(t *testing.T) {
+	_, err := ReadVersion(filepath.Join(t.TempDir(), "pyproject.toml"))
+	if err == nil {
+		t.Error("expected error for missing file")
+	}
+}
+
+func TestReadVersionNoVersion(t *testing.T) {
+	_, err := ReadVersion(writePyproject(t, `[build-system]
+requires = ["hatchling"]
+`))
+	if err == nil {
+		t.Error("expected error when no version is found")
+	}
+}
+
+// ── WriteVersion ──────────────────────────────────────────────────────────────
+
+func TestWriteVersionPEP621(t *testing.T) {
+	path := writePyproject(t, pyprojectPEP621)
+	if err := WriteVersion(path, "1.2.3", "1.2.4"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	data, _ := os.ReadFile(path)
+	s := string(data)
+	if !strings.Contains(s, `version = "1.2.4"`) {
+		t.Errorf("expected updated version; got:\n%s", s)
+	}
+	// build-system section must not be touched
+	if strings.Contains(s, `"hatchling>=1.2.4"`) {
+		t.Error("build-system section was incorrectly modified")
+	}
+}
+
+func TestWriteVersionPoetry(t *testing.T) {
+	path := writePyproject(t, pyprojectPoetry)
+	if err := WriteVersion(path, "1.2.3", "1.2.4"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	data, _ := os.ReadFile(path)
+	if !strings.Contains(string(data), `version = "1.2.4"`) {
+		t.Errorf("expected updated version; got:\n%s", data)
+	}
+}
+
+func TestWriteVersionBothSectionsUpdatesProject(t *testing.T) {
+	path := writePyproject(t, pyprojectBoth)
+	if err := WriteVersion(path, "1.2.3", "1.2.4"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	data, _ := os.ReadFile(path)
+	s := string(data)
+	// [project] version updated
+	if !strings.Contains(s, `[project]`) || strings.Index(s, `version = "1.2.4"`) > strings.Index(s, `[tool.poetry]`) {
+		t.Error("expected [project] version to be updated first")
+	}
+}
+
+func TestWriteVersionMissingFile(t *testing.T) {
+	err := WriteVersion(filepath.Join(t.TempDir(), "pyproject.toml"), "1.0.0", "1.0.1")
+	if err == nil {
+		t.Error("expected error for missing file")
+	}
+}
+
+func TestWriteVersionNotFound(t *testing.T) {
+	path := writePyproject(t, pyprojectPEP621)
+	err := WriteVersion(path, "9.9.9", "9.9.10")
+	if err == nil {
+		t.Error("expected error when old version not found")
+	}
+}
+
+func TestWriteVersionReadOnly(t *testing.T) {
+	if os.Getuid() == 0 {
+		t.Skip("skipping: chmod restrictions do not apply when running as root")
+	}
+	path := writePyproject(t, pyprojectPEP621)
+	os.Chmod(path, 0444)
+	defer os.Chmod(path, 0644)
+	if err := WriteVersion(path, "1.2.3", "1.2.4"); err == nil {
+		t.Error("expected error writing to read-only file")
+	}
+}
+
+// ── replaceVersion ────────────────────────────────────────────────────────────
+
+func TestReplaceVersionNotFound(t *testing.T) {
+	content := `[build-system]
+requires = ["hatchling"]
+`
+	got, ok := replaceVersion(content, "1.0.0", "1.0.1")
+	if ok {
+		t.Error("expected ok=false when no matching section")
+	}
+	if got != content {
+		t.Error("content should be unchanged when not found")
+	}
+}
+
+// ── fuzz ─────────────────────────────────────────────────────────────────────
+
+// FuzzReadVersion verifies ReadVersion never panics on arbitrary file content.
+func FuzzReadVersion(f *testing.F) {
+	f.Add(pyprojectPEP621)
+	f.Add(pyprojectPoetry)
+	f.Add(pyprojectBoth)
+	f.Add(`[project]` + "\n")
+	f.Add("")
+	f.Add("\x00\xff")
+
+	f.Fuzz(func(t *testing.T, content string) {
+		path := filepath.Join(t.TempDir(), "pyproject.toml")
+		os.WriteFile(path, []byte(content), 0644) //nolint:errcheck
+		ReadVersion(path)                          //nolint:errcheck
+	})
+}
+
+// FuzzWriteVersion verifies WriteVersion never panics on arbitrary content or version strings.
+func FuzzWriteVersion(f *testing.F) {
+	f.Add(pyprojectPEP621, "1.2.3", "1.2.4")
+	f.Add(pyprojectPoetry, "1.2.3", "1.2.4")
+	f.Add(pyprojectBoth, "1.2.3", "1.2.4")
+	f.Add("", "1.0.0", "1.0.1")
+	f.Add(`[project]`+"\n"+"version = \"1.0.0\"\n", "1.0.0", "1.0.1")
+
+	f.Fuzz(func(t *testing.T, content, oldVersion, newVersion string) {
+		path := filepath.Join(t.TempDir(), "pyproject.toml")
+		os.WriteFile(path, []byte(content), 0644)  //nolint:errcheck
+		WriteVersion(path, oldVersion, newVersion)  //nolint:errcheck
+	})
+}