Go running Python

Go running Python

Wednesday, January 4, 2017

Google runs millions of lines of Python code. The front-end server that drives youtube.com and YouTube’s APIs is primarily written in Python, and it serves millions of requests per second! YouTube’s front-end runs on CPython 2.7, so we’ve put a ton of work into improving the runtime and adapting our application to work optimally within it. These efforts have borne a lot of fruit over the years, but we always run up against the same issue: it’s very difficult to make concurrent workloads perform well on CPython.

To solve this problem, we investigated a number of other Python runtimes. Each had trade-offs and none solved the concurrency problem without introducing other issues.
So we asked ourselves a crazy question: What if we were to implement an alternative runtime optimized for real-time serving? Once we started going down the rabbit hole, Go seemed like an obvious choice of platform since its operational characteristics align well with our use case (e.g. lightweight threads). We wanted first class language interoperability and Go’s powerful runtime type reflection system made this straightforward. Python in Go felt very natural, and so Grumpy was born.

Grumpy is an experimental Python runtime for Go. It translates Python code into Go programs, and those transpiled programs run seamlessly within the Go runtime. We needed to support a large existing Python codebase, so it was important to have a high degree of compatibility with CPython (quirks and all). The goal is for Grumpy to be a drop-in replacement runtime for any pure-Python project.

Two design choices we made had big consequences. First, we decided to forgo support for C extension modules. This means that Grumpy cannot leverage the wealth of existing Python C extensions but it gave us a lot of flexibility to design an API and object representation that scales for parallel workloads. In particular, Grumpy has no global interpreter lock, and it leverages Go’s garbage collection for object lifetime management instead of counting references. We think Grumpy has the potential to scale more gracefully than CPython for many real world workloads. Results from Grumpy’s synthetic Fibonacci benchmark demonstrate some of this potential:

Second, Grumpy is not an interpreter. Grumpy programs are compiled and linked just like any other Go program. The downside is less development and deployment flexibility, but it offers several advantages. For one, it creates optimization opportunities at compile time via static program analysis. But the biggest advantage is that interoperability with Go code becomes very powerful and straightforward: Grumpy programs can import Go packages just like Python modules! For example, the Python snippet below uses Go’s standard net/http package to start a simple server:

from __go__.net.http import ListenAndServe, RedirectHandler

handler = RedirectHandler('http://github.com/google/grumpy', 303)
ListenAndServe('', handler)

We’re excited about the prospects for Grumpy. Although it’s still alpha software, most of the language constructs and many core built-in types work like you’d expect. There are still holes to fill — many built-in types are missing methods and attributes, built-in functions are absent and the standard library is virtually empty. If you find things that you wish were working, file an issue so we know what to prioritize. Or better yet, submit a pull request.

Stay Grumpy!

By Dylan Trotter, YouTube Engineering


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