November 10, 2020

Making The Case For A (Semi) Formal Specification Of CPython

36 minutes

Summary

The CPython implementation has grown and evolved significantly over the past ~25 years. In that time there have been many other projects to create compatible runtimes for your Python code. One of the challenges for these other projects is the lack of a fully documented specification of how and why everything works the way that it does. In the most recent Python language summit Mark Shannon proposed implementing a formal specification for CPython, and in this episode he shares his reasoning for why that would be helpful and what is involved in making it a reality.

Announcements

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Your host as usual is Tobias Macey and today I’m interviewing Mark Shannon about his efforts to create a formal specification for the CPython interpreter

Interview

Introductions

How did you get introduced to Python?

Can you start by describing the current state of how the Python language and the CPython runtime are defined?

What is your motivation in advocating for a specification?

After ~25 years of the language, why is now the time to pursue this effort?

How does the history of the language and the scope of the ecosystem and community impact the effort required to make this a reality?

What is involved in creating the specification and where would it be located once complete?

What are some examples of languages that are formally specified?

What are the possible benefits of creating a specification for the CPython virtual machine?

What is the distinction between a specification for the VM as opposed to a specification for the language?

What are some potential downsides to having a (semi-)formal specification become part of the definition of the interpreter?

Can you describe the process of doing the work to create the specification?

How are you approaching the actual definition of the specification (e.g. prose vs programmatic)?

What are the tradeoffs of prose vs. an executable specification (e.g. TLA+, Alloy)?

How does this work tie into your goals of improving the speed of the CPython interpreter?

What are some of the most interesting, unexpected, or challenging aspects of your efforts to bring this specification to CPython?

How can the community contribute to this effort?

Keep In Touch

markshannon on GitHub

Website

Picks

Tobias

American Gods book and TV series

Mark

Roadside Picnic

In Death (VR game)

–On Steam

Closing Announcements

Thank you for listening! Don’t forget to check out our other show, the Data Engineering Podcast for the latest on modern data management.

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Links

CPython

PyPy

PEP 380 yield from

Language Summit

RustPython

Jython

C++

ML programming language

Java

Python Formal Semantics git repository

CPython PEG Parser Episode with Pablo Galindo and Lysandros Nikolaou

IETF RFCs

The intro and outro music is from Requiem for a Fish The Freak Fandango Orchestra / CC BY-SA

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By Tobias Macey

4.4

100100 ratings