gevent

gevent is a Python networking library that provides a coroutine-based API for asynchronous I/O using greenlets. It allows writing scalable, I/O-bound network code in a synchronous style by executing many lightweight tasks, or greenlets, within a single Python process.

At its core, gevent uses the greenlet library for lightweight coroutines and a libev-based event loop to monitor I/O and timers. It also offers monkey patching through gevent.monkey, which replaces blocking parts of the Python standard library (such as socket, ssl, select, and threading) with cooperative equivalents, enabling existing blocking code to run non-blocking without extensive rewrites.

gevent provides a range of components for building network applications, including a WSGI server (gevent.pywsgi), an asynchronous HTTP client, and a collection of utilities (Pool, Queue, Event) that work with greenlets. The library exposes socket-like objects and DNS resolution that integrate with the event loop for high concurrency.

gevent is designed to work with CPython and PyPy, but it does not remove the Python Global Interpreter Lock. Concurrency is achieved through cooperative multitasking of greenlets, and CPU-bound workloads will not automatically run in parallel. To scale across processors, deployment typically uses multiple processes or additional parallelism strategies.

Limitations and considerations include potential incompatibilities with libraries that perform blocking operations outside of gevent's control, or with native extensions that do not cooperate with monkey patching. When using gevent, it is common to patch the standard library at startup to ensure full non-blocking behavior.