Python Bytes
Python Bytes
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Python Bytes is a weekly podcast hosted by Michael Kennedy and Brian Okken. The show is a short discussion on the headlines and noteworthy news in the Python, developer, and data science space.

#434 Most of OpenAI’s tech stack runs on Python

June 02, 2025 00:29:01 5.24 MB ( 22.8 MB less) Downloads: 0
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Brian #1: Making PyPI’s test suite 81% faster

  • Alexis Challande
  • The PyPI backend is a project called Warehouse
  • It’s tested with pytest, and it’s a large project, thousands of tests.
  • Steps for speedup
    • Parallelizing test execution with pytest-xdist
      • 67% time reduction
      • --numprocesses=auto allows for using all cores
      • DB isolation - cool example of how to config postgress to give each test worker it’s on db
      • They used pytest-sugar to help with visualization, as xdist defaults to quite terse output
    • Use Python 3.12’s sys.monitoring to speed up coverage instrumentation
      • 53% time reduction
      • Nice example of using COVERAGE_CORE=sysmon
    • Optimize test discovery
      • Always use testpaths
      • Sped up collection time. 66% reduction (collection was 10% of time)
      • Not a huge savings, but it’s 1 line of config
    • Eliminate unnecessary imports
      • Use python -X importtime
      • Examine dependencies not used in testing.
      • Their example: ddtrace
        • A tool they use in production, but it also has a couple pytest plugins included
        • Those plugins caused ddtrace to get imported
        • Using -p:no ddtrace turns off the plugin bits
  • Notes from Brian:
    • I often get questions about if pytest is useful for large projects.
    • Short answer: Yes!
    • Longer answer: But you’ll probably want to speed it up
    • I need to extend this article with a general purpose “speeding up pytest” post or series.
    • -p:no can also be used to turn off any plugin, even builtin ones.
      • Examples include
        • nice to have developer focused pytest plugins that may not be necessary in CI
        • CI reporting plugins that aren’t needed by devs running tests locally

Michael #2: People aren’t talking enough about how most of OpenAI’s tech stack runs on Python

  • Original article: Building, launching, and scaling ChatGPT Images
  • Tech stack: The technology choices behind the product are surprisingly simple; dare I say, pragmatic!
    • Python: most of the product’s code is written in this language.
    • FastAPI: the Python framework used for building APIs quickly, using standard Python type hints. As the name suggests, FastAPI’s strength is that it takes less effort to create functional, production-ready APIs to be consumed by other services.
    • C: for parts of the code that need to be highly optimized, the team uses the lower-level C programming language
    • Temporal: used for asynchronous workflows and operations inside OpenAI. Temporal is a neat workflow solution that makes multi-step workflows reliable even when individual steps crash, without much effort by developers. It’s particularly useful for longer-running workflows like image generation at scale

Michael #3: PyCon Talks on YouTube

Brian #4: Optimizing Python Import Performance

  • Mostly pay attention to #'s 1-3
  • This is related to speeding up a test suite, speeding up necessary imports.
  • Finding what’s slow
    • Use python -X importtime <the reset of the command
    • Ex: python -X importtime ptyest
  • Techniques
    • Lazy imports
      • move slow-to-import imports into functions/methods
    • Avoiding circular imports
      • hopefully you’re doing that already
    • Optimize __init__.py files
      • Avoid unnecessary imports, heavy computations, complex logic
  • Notes from Brian
    • Some questions remain open for me
      • Does module aliasing really help much?
    • This applies to testing in a big way
      • Test collection imports your test suite, so anything imported at the top level of a file gets imported at test collection time, even if you only are running a subset of tests using filtering like -x or -m or other filter methods.
      • Run -X importtime on test collection.
      • Move slow imports into fixtures, so they get imported when needed, but NOT at collection.
  • See also:

Extras

Brian:

  • PEPs & Co.
    • PEP is a ‘backronym”, an acronym where the words it stands for are filled in after the acronym is chosen. Barry Warsaw made this one up.
    • There are a lot of “enhancement proposal” and “improvement proposal” acronyms now from other communities
  • pythontest.com has a new theme
    • More colorful. Neat search feature
    • Now it’s excruciatingly obvious that I haven’t blogged regularly in a while
      • I gotta get on that
    • Code highlighting might need tweaked for dark mode

Michael:

Joke: There is hope.

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