Brought to you by Michael and Brian - take a Talk Python course or get Brian's pytest book

#296: pip: Constrain your excitement

Published Tue, Aug 9, 2022, recorded Tue, Aug 9, 2022
Watch this episode on YouTube
Play on YouTube
Watch the live stream replay

About the show

Sponsored by the IRL Podcast from Mozilla

Brian #1: Pip constraints files

  • by luminousmen
  • You can put some constraints on your dependencies with a constraints file.
  • “Constraints files are requirements files that only control which version of a requirement is installed, not whether it is installed or not. “
  • Syntax is a subset of requirements.txt syntax
    • but all the restrictions seem reasonable, considering
      • must have a name
      • can’t be editable
      • can’t specify extras (that one is maybe slightly weird)
  • You can put --constraint constraints.txt right at the top of your requirements.txt file
  • or specify it on command line,
    • pip install --constraint constraints.txt -r requirements.txt
  • Or, my favorite, stick it at the top of file.
    • yes. pip-compile correctly handles constraints when generating requirements.txt.
  • Example
    • --constraint constraints.txt typer
    • constraints.txt click<8.1.3
    • Output from pip-compile
      # This file is autogenerated by pip-compile with python 3.10
      # To update, run:
      #    pip-compile
          # via
          #   -c constraints.txt
          #   typer
          # via -r

Michael #2: async-cache

  • A caching solution for asyncio
  • Quite simple but looks effective and flexible too
  • Example:
    # TTL Cache
    from cache import AsyncTTL
    @AsyncTTL(time_to_live=60, maxsize=1024)
    async def func(*args, **kwargs):
        time_to_live : max time for which a cached result  is valid
        maxsize : max number of results that are cached.
                    if  max limit  is reached the oldest result  is deleted.

Brian #3: Organize Python code like a PRO

  • Guilherme Latrova
  • Yes, this is one author’s opinion. but…
    • lots of great advice
    • nothing too weird
    • no tool recommendations
  • Recommendations of note
    • keep a src dir.
      • A cool and simple reason: it keeps your source code together in alphabetized IDEs.
    • file/module names: plural except for config, main, core, or similar
      • slightly weird tangent that there are no files, there are modules. ok, whatever.
      • Also talking about directories as main modules. odd. but ok.
    • functions/methods should be verbs
    • variables/constants should be nouns
    • Class names should be singular, unless the class really represents a container
    • The __name__ == "__main__" trick for modules.
    • The entry point trick for modules/packages so that -m mymodule does something.
  • -

Michael #4: keyring

  • via Trent
  • The Python keyring library provides an easy way to access the system keyring service from python. It can be used in any application that needs safe password storage.
  • It’s also helpful in that it allows you to write your own backends. Useful for testing.
  • Basically create a dummy keychain that stores to a pytest temp_path fixture instead of cluttering the real keychain.
  • You could potentially write a backend to interact with any service such as 1Password.



  • I’m taking a class on FastAPI. The instructor is awesome!
  • Also, editing some pytest course video.



  • from a dad-jokes repo
    • Q: How do programming pirates pass method parameters?
    • A: Varrrrarrrgs.
    • Q: How do you get the code for the bank vault?
    • A: You checkout their branch.
    • "Unfortunately these jokes only work if you git them."
  • Screw driver

Want to go deeper? Check our projects