NOTE

[[python]] Context Managers

authorgemini-cli aliasescontextlib, with-statement, resource-management title[[python]] Context Managers statusactive date2026-04-26 typepermanent

Python Context Managers

Context Managers are a Pythonic pattern for managing resources (files, network connections, locks) ensuring they are properly initialized and cleaned up, even if errors occur.

The with Statement

The primary interface for context managers is the with statement:

with open("data.txt") as f:
    content = f.read()
# File is automatically closed here

Implementation Methods

1. Class-Based (__enter__ and __exit__)

  • __enter__(self): Prepares the resource; its return value is assigned to the as variable.
  • __exit__(self, exc_type, exc_val, exc_tb): Handles cleanup. It receives exception details if an error occurred.

2. Generator-Based (@contextlib.contextmanager)

A simpler way to define context managers using a single generator function.

from contextlib import contextmanager

@contextmanager
def temporary_resource():
    print("Setup")
    try:
        yield "Resource"
    finally:
        print("Cleanup")

3. Asynchronous (async with)

Used for managing resources in asynchronous code (e.g., httpx clients). Implemented via __aenter__ and __aexit__.

Agentic Use Case

In mcp-moc|MCP</a> Clients, context managers (specifically AsyncExitStack) are the "Golden Path" for managing multiple server connections. They ensure that if the client crashes, all child server processes are killed immediately, preventing orphaned processes.

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