Why Python is Slow: Antonio Cuni on SPy and Statically Compiled Python [Full Episode]
Antonio Cuni (principal engineer at Anaconda, author of SPy, developer of PyScript and PyPy, co-founder of the HPy project, and creator of PDB++, Fancy Completer, and VMProf) shares why Python is slow and how SPy, a new statically compiled variant of Python, aims to be as fast as C while staying as Pythonic as Python. We discuss the trade-off between dynamic features and performance, how SPy's "red and blue" code model replaces best-effort JIT with predictable errors, why PyPy struggles with C extensions, and what "Pythonic" really means.
Outline
00:00 - Episode highlights and introduction
00:40 - Why is Python so slow?
01:31 - Would a static Python be fast?
02:13 - What is SPy?
02:28 - What motivated you to create SPy? (Spoiler: frustration)
03:52 - Which ideas from PyPy and HPy went into SPy?
06:36 - Biggest challenges of building SPy
07:49 - What does "Pythonic" actually mean?
10:39 - Current roadmap and the two-level language idea
12:24 - Walking through the SPy compilation pipeline
13:57 - Red-shifting and the blue/red AST nodes
14:40 - Why blue and red? (No, it's not from The Matrix)
15:52 - PyPy vs SPy: when to use which
19:34 - C extensions and the C API problem
20:04 - How to actually make your Python code faster
23:34 - Memory management and garbage collection in SPy
24:44 - When will SPy be production-ready?
25:44 - How to contribute to SPy
26:26 - Where does the name "SPy" come from?
🎙️ This episode was recorded live at EuroPython in July 2025 in Prague.
Episode links
– SPy on GitHub: https://github.com/spylang/spy
– PyPy: https://pypy.org/
– HPy project: https://hpyproject.org/
– PyScript: https://pyscript.net/
– Anaconda: https://www.anaconda.com/
– decorators in SPy: https://github.com/spylang/spy/pull/225
– SPy roadmap: https://github.com/spylang/spy/blob/m...
– list type in SPy: https://github.com/spylang/spy/blob/m...
– garbage collector in SPy: https://github.com/spylang/spy/pull/390
– SPy documentation: https://spylang.github.io/docs/dev/
– series of blog posts on SPy: https://antocuni.eu/2025/10/29/inside...
Where to listen
– Spotify: https://open.spotify.com/show/2Z9Ewkd...
– Apple Podcasts: https://podcasts.apple.com/podcast/id...
– RSS feed: https://media.rss.com/behindthecommit...