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Packaging and Dependency Management

A talk given by Craig Kerstiens at PyCodeConf 2011.

Outline

  • Why It Matters

    • Rapid bootstrapping
    • Predictable behavior
    • Deployment

  • Packaging

    • Tool is distutils
    • Write a setup script
    • Creating a source distribution
    • Release it
      • BUT WHERE?

  • Release options

    • Your server
      • You get full control
      • People rely on your availability
      • Don't do this
    • GitHub
      • Awesome for development
      • Awesome for collaboration
      • Not awesome for release
      • Not an appropriate vehicle for release
    • PyPi - The Cheese Shop
      • Host it here
      • If it's down, the entire community knows
      • There's mirrors for a reason

  • Managing dependencies

    • Old tools: easy_setup
    • New tools: pip and virtualenv
    • pip benefits
      • Supports uninstalling
      • Lots of small improvements
      • Supports version control (don't do this in production)
    • virtualenv benefits
      • Tool for creating isolated Python environment
      • Creates local sandbox of environment
      • Destroy and recreate often

  • Tips for Packaging

    • Be explicit with version numbers in dependencies

    • It should be absoluting explicit - it is very easy to do

      pip freeze > requirements.txt
cat requirements.txt

    • PyPi's down

      pip install --use-mirrors

  • What's missing

    • Bundler
      • Gemfile
      • Gemfile.lock
    • Pip needs a cleaner upgrade

Questions

  • Why isn't --use-mirrors the default?
    • Next release it will be
  • How do you handle versions of dependencies of dependencies?
    • Pip 3 will take care of this for you? Using Pip freeze will take care of everything
  • How do I use setup.py with respect to requirements.txt?
    • requirements.txt is the canonical way going forward.
  • On Heroku, when you deploy, is it using requirements.txt?
    • It absolutely is - you'll always know what it is going to do on Heroku.

References