Agent skill
stdlib-scripting
LAST RESORT for stdlib-only Python 3.11+ scripts in CONFIRMED restricted environments (airgapped systems, no uv, no internet access). Creates portable dependency-free scripts using argparse, logging, config management (JSON/TOML/INI), and cross-platform patterns. Use ONLY when environment restrictions prevent Typer+Rich with PEP 723. Triggers on "stdlib-only script", "no dependencies", "airgapped", "restricted environment", "portable script no network". For standard CLI development, use python-cli-architect with Typer+Rich instead.
Install this agent skill to your Project
npx add-skill https://github.com/Jamie-BitFlight/claude_skills/tree/main/plugins/python3-development/skills/stdlib-scripting
SKILL.md
Stdlib Scripting
Positioning
This skill is a LAST RESORT. Use ONLY when confirmed environment restrictions prevent dependency installation.
flowchart TD
Start([Need Python CLI script]) --> Q1{Environment allows network access<br>for dependency installation?}
Q1 -->|Yes — standard environment| UseTyper[Use python-cli-architect with Typer+Rich<br>Less code, better UX, well-tested libraries]
Q1 -->|No — restricted environment| Q2{Restriction type confirmed?}
Q2 -->|No — assumption only| Stop[STOP — Verify with user first<br>Do not assume restrictions]
Q2 -->|Yes — airgapped/no internet/no uv| StdLib[Use stdlib-scripting<br>Maximum portability, basic UX]
UseTyper --> Why1[Why: PEP 723 + uv handles dependencies<br>Simpler code, richer features]
StdLib --> Why2[Why: Runs anywhere Python 3.11+ installed<br>More code to write and maintain]
See ../python3-development/SKILL.md#script-dependency-trade-offs in parent skill for detailed comparison.
Role
Create portable, dependency-free Python 3.11+ scripts that use only standard library at runtime. All code passes ruff check and the project type checker (ty or mypy / pyright per repo), with comprehensive pytest coverage.
Fundamental principle: Patterns are tools, not goals. Prefer simplicity, clarity, maintainability, and pragmatism over pattern correctness.
Dependency Policy
- Runtime: Standard library ONLY (no external packages)
- Dev-only: pytest, ruff, ty (preferred), mypy or pyright when matching the host project
- Runtime exceptions: Only if essential, with explicit written justification and pinning strategy
Working Process
PHASE 0: Research
- Grep existing codebase for patterns to reuse
- List edge cases, integration points, and permission issues
PHASE 1: Refactor Sanity Check
- Measure lines, branches, redundancy, and readability
- Apply only changes that reduce duplication or improve clarity
- Walrus, DRY, SRP rules enforced with justification
Required report:
REFACTORING IMPACT ANALYSIS:
- Line count: X -> Y (∆ Z)
- Functions affected: N
- Patterns applied: [...]
- Complexity reduction: [...]
- Rejected changes: [reasons]
PHASE 2: Creation
- Confirm Python 3.11+ requirement
- Ensure no forbidden typing imports
- Design: argparse CLI, structured logging, error boundaries, config handling
- Async only for I/O-bound operations
PHASE 3: Validation
Automated:
python -m py_compile <file>
grep -E "from typing import .*(Dict|List|Set|Tuple|Optional|Union)\b" <file>
ruff check <file>
# Type check: match the host project — ty is default in this repo (`uv run ty check <file>`);
# use `mypy --strict <file>` when the project standardizes on mypy or uv is unavailable.
Checklist:
- ✅ Docstrings present
- ✅ CLI help works
- ✅ Unit tests for normal, edge, and error paths
- ✅ Cross-platform path handling
- ✅ Validation output shown
Validation output (required):
VALIDATION REPORT:
✅ Syntax check: PASSED
✅ Forbidden patterns: NONE FOUND
✅ Native type hints: VERIFIED (X instances)
✅ Ruff: PASSED
✅ Type check (ty or mypy): PASSED
✅ Checklist items: COMPLETED
Code Quality Standards
- Pass
ruff checkand type checking clean (tyormypy --strictper project) - Google-style docstrings for modules, classes, and functions
- Use structural pattern matching, dataclasses, and walrus operator only if they reduce complexity and increase clarity
- Follow PEP 8
System Integration Patterns
Privileged Command Execution
from shutil import which
import os, subprocess
def run_privileged_command(cmd: str, args: list[str]) -> subprocess.CompletedProcess[str]:
if os.name != "posix":
return subprocess.run([cmd, *args], capture_output=True, text=True)
if os.geteuid() == 0:
full = [cmd, *args]
elif (sudo := which("sudo")):
full = [sudo, "-n", cmd, *args]
else:
full = [cmd, *args]
return subprocess.run(full, capture_output=True, text=True, check=False)
CLI
import argparse
def create_parser() -> argparse.ArgumentParser:
parser = argparse.ArgumentParser(
description="Tool description",
formatter_class=argparse.RawDescriptionHelpFormatter,
)
return parser
Logging
import logging
from pathlib import Path
def setup_logging(level: str = "INFO", log_file: Path | None = None) -> None:
handlers: list[logging.Handler] = [logging.StreamHandler()]
if log_file:
handlers.append(logging.FileHandler(log_file))
logging.basicConfig(
level=getattr(logging, level.upper(), logging.INFO),
format="%(asctime)s %(name)s %(levelname)s %(message)s",
handlers=handlers,
)
Config
import json, configparser, tomllib
from pathlib import Path
from typing import Any
def load_config(path: Path) -> dict[str, Any]:
ext = path.suffix.lower()
data = path.read_text()
if ext == ".json":
return json.loads(data)
if ext == ".toml":
return tomllib.loads(data)
if ext in (".ini", ".cfg"):
p = configparser.ConfigParser()
p.read_string(data)
return {sec: dict(p[sec]) for sec in p.sections()}
raise ValueError(f"Unsupported config format: {ext}")
Errors
import logging, sys
class ScriptError(Exception):
"""Base error for script-related failures."""
def handle_error(err: Exception, logger: logging.Logger) -> None:
logger.error(f"Error: {err}")
if logger.isEnabledFor(logging.DEBUG):
logger.exception("Traceback")
sys.exit(1)
Async
import asyncio
from collections.abc import Coroutine
from typing import Any
async def run_async(tasks: list[Coroutine[Any, Any, Any]]) -> list[Any]:
return await asyncio.gather(*tasks, return_exceptions=True)
Multi-File Project Skeleton
When PEP 723 single-file approach is insufficient:
project_name/
├── main.py
├── core/
│ ├── __init__.py
│ ├── config.py
│ ├── logging_setup.py
│ └── exceptions.py
├── utils/
│ ├── __init__.py
│ └── helpers.py
├── tests/
│ ├── __init__.py
│ ├── test_main.py
│ └── test_core.py
├── config.example.toml
└── README.md
Testing Standards
Pytest with coverage of normal, edge, and error cases.
import json
from pathlib import Path
from module import load_config
def test_load_json(tmp_path: Path) -> None:
path = tmp_path / "c.json"
path.write_text(json.dumps({"k": "v"}))
result = load_config(path)
assert result == {"k": "v"}
Shebang and PEP 723 Validation
For ALL Python scripts you create or modify, validate the shebang:
/python3-development:shebangpython <file_path>
This ensures stdlib-only scripts use #!/usr/bin/env python3 without PEP 723 metadata (nothing to declare).
Detailed Reference Material
Typing guidance, protocols, type aliases, and advanced patterns:
references/typing-strategy.md- Protocol vs TypeVar vs ParamSpec, abstract collections, Any boundaries, JSON handlingreferences/command-execution.md- Timeout handling, privilege elevation, logging, type-safe command buildingreferences/type-safety-patterns.md- Overloads, protocols, type narrowing, linter settings
Boundaries
- No deprecated syntax
- No platform-specific behavior without fallbacks
- No skipping validation or tests
- No delivery without a full Validation Report
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