pyrift

Detect silent Python behaviour differences across CPython versions and CPython vs PyPy.

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What is pyrift?

Python upgrades and cross-runtime compatibility (CPython vs PyPy) introduce silent behaviour differences — code that runs without errors but produces wrong results, leaks resources, or crashes only in certain environments.

These are not syntax errors. Linters won't catch them. They are not CVEs. Security scanners won't catch them. They only appear at runtime, often in production.

pyrift statically detects these patterns before they become bugs.

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Install

pip install pyrift

Zero external dependencies. Pure Python. Works on Python 3.10+.

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Quick start — CLI

# Scan current directory
pyrift scan .

# Scan a specific path
pyrift scan ./src

# JSON output (for CI integration)
pyrift scan . --format json

# Markdown report saved to file
pyrift scan . --format markdown --output report.md

# Check version
pyrift --version

Example output

[ERROR] src/server.py:42 CPY002: Exception.add_note() requires Python 3.11+
→ Guard with: if sys.version_info >= (3, 11): e.add_note(...)

[ERROR] src/compat.py:17 CPY007: Module removed in Python 3.13
→ Find a third-party replacement for 'cgi' on PyPI

[WARNING] src/resource.py:88 PPY001: Relying on del for resource cleanup breaks on PyPy
→ Use context managers (with statement) or try/finally blocks

Scanned 23 file(s). Found 2 error(s), 1 warning(s). Score: 77/100

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Quick start — Python API

import pyrift

# Scan a directory
result = pyrift.scan("./src")

print(result)
# ScanResult(files=23, errors=2, warnings=1, score=77)

# Iterate findings
for finding in result.findings:
    print(finding)

# Filter by severity
for error in result.errors:
    print(f"{error.file}:{error.line} — {error.title}")

# Export formats
json_output     = pyrift.to_json(result)
markdown_output = pyrift.to_markdown(result)
text_output     = pyrift.to_text(result)

# Scan a single file
findings = pyrift.scan_file("./src/utils.py")

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Rules

CPython rules — version compatibility

ID	Title	Severity	Affects
CPY001	Dict ordering assumption	Warning	CPython < 3.7
CPY002	Exception.add_note() requires Python 3.11+	Error	CPython ≤ 3.10
CPY003	X | Y union type syntax requires Python 3.10+	Error	CPython ≤ 3.9
CPY004	tomllib requires Python 3.11+	Error	CPython ≤ 3.10
CPY005	match/case requires Python 3.10+	Error	CPython ≤ 3.9
CPY006	asyncio.timeout() / TaskGroup requires Python 3.11+	Error	CPython ≤ 3.10
CPY007	Module removed in Python 3.13 (21 modules)	Error	CPython ≥ 3.13
CPY008	__slots__ may not prevent __dict__ with base classes	Info	All versions
CPY009	ExceptionGroup requires Python 3.11+	Error	CPython ≤ 3.10
CPY010	@dataclass(slots=True) requires Python 3.10+	Error	CPython ≤ 3.9

PyPy rules — runtime differences

ID	Title	Severity	Affects
PPY001	Relying on __del__ for resource cleanup	Error	PyPy all versions
PPY002	ctypes usage may silently fail	Warning	PyPy all versions
PPY003	sys.getrefcount() is meaningless on PyPy	Error	PyPy all versions
PPY004	weakref.proxy() raises ReferenceError unpredictably	Warning	PyPy all versions
PPY005	File write without explicit flush may lose data	Warning	PyPy all versions
PPY006	Monkey-patching built-in types behaves differently	Warning	PyPy all versions
PPY007	sys.intern() identity guarantees differ on PyPy	Warning	PyPy all versions

Full rule documentation: docs/rules.md

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Use in CI

Add pyrift to your GitHub Actions workflow:

- name: Run pyrift
  run: |
    pip install pyrift
    pyrift scan . --format json --output pyrift-report.json
    pyrift scan .

Exit code is 1 when errors are found — fails the CI build automatically. Use --exit-zero to report without failing.

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Use with pre-commit

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/BHUVANSH855/pyrift
    rev: v0.3.1
    hooks:
      - id: pyrift

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Why pyrift?

Tool	What it catches	What it misses
pylint / ruff	Style, common bugs	Runtime behaviour differences
mypy / pyright	Type errors	Runtime behaviour differences
pip-audit	Known CVEs	Behaviour differences
bandit	Security patterns	Behaviour differences
pyrift	Silent runtime behaviour differences	(that's the whole point)

pyrift does not replace any of these tools. It catches what they all miss.

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Roadmap

Planned for upcoming versions — contributions welcome:

• CPY011 — typing.Self requires Python 3.11+
• CPY012 — typing.LiteralString requires Python 3.11+
• CPY013 — @override decorator requires Python 3.12+
• PPY008 — array.array behaviour differences on PyPy
• PPY009 — decimal module precision differences on PyPy
• Pre-commit hook native support
• VS Code extension
• GitHub Action marketplace listing

See CONTRIBUTING.md to add a rule yourself — rule IDs CPY011+ and PPY008+ are open for community contributions.

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Contributing

Contributions are very welcome — especially new rules for behaviour differences you have personally encountered.

See CONTRIBUTING.md for the full guide.

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Project status

• Version: 0.3.1
• Rules: 17 (10 CPython + 7 PyPy)
• Tests: 70 passing
• Dependencies: zero
• Python: 3.10+

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Author

Built by Bhuvansh Kataria — CPython contributor and PyPy toolkit author.

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License

MIT — see LICENSE