website/content/blog/gevent.md
2020-04-09 17:59:56 -04:00

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---
title: "Gevent"
date: 2020-04-09T17:22:52-04:00
draft: false
tags: ["python", "concurrency"]
---
In my last post I spoke about [concurrency with asyncio](https://brandonrozek.com/blog/pyasyncio/). Now what if you don't want to concern yourself with async/await practices and just want to write synchronous code that executes I/O asynchronously? That's where the library [gevent](http://www.gevent.org/) comes in. It does this by modifying Python's standard library during runtime to call it's own asynchronous versions.
Last post code's example written in `gevent`.
```python
# The first two lines must be called before
# any other modules are loaded
import gevent
from gevent import monkey; monkey.patch_all()
import time
def think(duration):
print("Starting to think for " + str(duration) + " seconds...")
time.sleep(duration)
print("Finished thinking for " + str(duration) + " seconds...")
gevent.wait([
gevent.spawn(think, 5),
gevent.spawn(think, 2)
])
```
Notice that the function `think` is written the same as the synchronous version.
`gevent` is written on top of C libraries `libev` or `libuv` . This combined with the monkey patching can make `gevent` based applications hard to debug if something goes wrong. Otherwise it's a great tool to quickly take advantage of concurrency.