Python Resource Management

When to use this skill

Use Python Resource Management when an AI agent needs a reusable SKILL.md workflow for this job: Python resource management with context managers, cleanup patterns, and streaming. Use when managing connections, file handles, implementing cleanup logic, or building streaming responses with accumulated state.

When not to use it

Skip Python Resource Management when the task is outside the coding category, or when a more specific skill in this directory already covers the same workflow with clearer triggers.

How to install

1. Personal install: create ~/.claude/skills/python-resource-management/SKILL.md (and any bundled scripts) so Claude Code, Claude Desktop, and compatible agents can load it in every project.
2. Project install: commit the same folder at .claude/skills/python-resource-management/ so teammates get the skill with the repo.
3. Restart the agent session after copying files so it re-scans the skills directory, then ask for the task in words that match the skill description.

Full install guide for Claude, Cursor, and Codex

What this skill does

# Python Resource Management

Manage resources deterministically using context managers. Resources like database connections, file handles, and network sockets should be released reliably, even when exceptions occur.

## When to Use This Skill

- Managing database connections and connection pools - Working with file handles and I/O - Implementing custom context managers - Building streaming responses with state - Handling nested resource cleanup - Creating async context managers

## Core Concepts

### 1. Context Managers

The `with` statement ensures resources are released automatically, even on exceptions.

### 2. Protocol Methods

`__enter__`/`__exit__` for sync, `__aenter__`/`__aexit__` for async resource management.

### 3. Unconditional Cleanup

`__exit__` always runs, regardless of whether an exception occurred.

### 4. Exception Handling

Return `True` from `__exit__` to suppress exceptions, `False` to propagate them.

## Quick Start

```python from contextlib import contextmanager

@contextmanager def managed_resource(): resource = acquire_resource() try: yield resource finally: resource.cleanup()

with managed_resource() as r: r.do_work() ```

## Fundamental Patterns

### Pattern 1: Class-Based Context Manager

Implement the context manager protocol for complex resources.

```python class DatabaseConnection: """Database connection with automatic cleanup."""

def __init__(self, dsn: str) -> None: self._dsn = dsn self._conn: Connection | None = None

def connect(self) -> None: """Establish database connection.""" self._conn = psycopg.connect(self._dsn)

def close(self) -> None: """Close connection if open.""" if self._conn is not None: self._conn.close() self._conn = None

def __enter__(self) -> "DatabaseConnection": """Enter context: connect and return self.""" self.connect() return self

def __exit__( self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None, ) -> None: """Exit context: always close connection.""" self.close()

# Usage with context manager (preferred) with DatabaseConnection(dsn) as db: result = db.execute(query)

# Manual management when needed db = DatabaseConnection(dsn) db.connect() try: result = db.execute(query) finally: db.close() ```

### Pattern 2: Async Context Manager

For async resources, implement the async protocol.

```python class AsyncDatabasePool: """Async database connection pool."""

def __init__(self, dsn: str, min_size: int = 1, max_size: int = 10) -> None: self._dsn = dsn self._min_size = min_size self._max_size = max_size self._pool: asyncpg.Pool | None = None

async def __aenter__(self) -> "AsyncDatabasePool": """Create connection pool.""" self._pool = await asyncpg.create_pool( self._dsn, min_size=self._min_size, max_size=self._max_size, ) return self

async def __aexit__( self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None, ) -> None: """Close all connections in pool.""" if self._pool is not None: await self._pool.close()

async def execute(self, query: str, *args) -> list[dict]: """Execute query using pooled connection.""" async with self._pool.acquire() as conn: return await conn.fetch(query, *args)

# Usage async with AsyncDatabasePool(dsn) as pool: users = await pool.execute("SELECT * FROM users WHERE active = $1", True) ```

### Pattern 3: Using @contextmanager Decorator

Simplify context managers with the decorator for straightforward cases.

```python from contextlib import contextmanager, asynccontextmanager import time import structlog

logger = structlog.get_logger()

@contextmanager def timed_block(name: str): """Time a block of code.""" start = time.perf_counter() try: yield finally: elapsed = time.perf_counter() - start logger.info(f"{name} completed", duration_seconds=round(elapsed, 3))

# Usage with timed_block("data_processing"): process_large_dataset()

@asynccontextmanager async def database_transaction(conn: AsyncConnection): """Manage database transaction.""" await conn.execute("BEGIN") try: yield conn await conn.execute("COMMIT") except Exception: await conn.execute("ROLLBACK") raise

# Usage async with database_transaction(conn) as tx: await tx.execute("INSERT INTO users ...") await tx.execute("INSERT INTO audit_log ...") ```

### Pattern 4: Unconditional Resource Release

Always clean up resources in `__exit__`, regardless of exceptions.

```python class FileProcessor: """Process file with guaranteed cleanup."""

def __init__(self, path: str) -> None: self._path = path self._file: IO | None = None self._temp_files: list[Path] = []

def __enter__(self) -> "FileProcessor": self._file = open(self._path, "r") return self

def __exit__( self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None, ) -> None: """Clean up all resources unconditionally.""" # Close main file if self._file is not None: self._file.close()

# Clean up any temporary files for temp_file in self._temp_files: try: temp_file.unlink() except OSError: pass # Best effort cleanup

# Return None/False to propagate any exception ```

## Detailed worked examples and patterns

Detailed sections (starting with `## Advanced Patterns`) live in `references/details.md`. Read that file when the navigation summary above is insufficient.

## Best Practices Summary

1. **Always use context managers** - For any resource that needs cleanup 2. **Clean up unconditionally** - `__exit__` runs even on exception 3. **Don't suppress unexpectedly** - Return `False` unless suppression is intentional 4. **Use @contextmanager** - For simple resource patterns 5. **Implement both protocols** - Support `with` and manual management 6. **Use ExitStack** - For dynamic numbers of resources 7. **Accumulate efficiently** - List + join, not string concatenation 8. **Track metrics** - Time-to-first-byte matters for streaming 9. **Document behavior** - Especially exception suppression 10. **Test cleanup paths** - Verify resources are released on errors

Intended uses

• Managing database connections and connection pools
• Working with file handles and I/O
• Implementing custom context managers
• Building streaming responses with state
• Handling nested resource cleanup
• Creating async context managers