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Set PYTHONPYCACHEPREFIX to /tmp during build phase. #442

Merged
merged 2 commits into from
Oct 25, 2022
Merged

Set PYTHONPYCACHEPREFIX to /tmp during build phase. #442

merged 2 commits into from
Oct 25, 2022

Commits on Oct 25, 2022

  1. Set PYTHONPYCACHEPREFIX to /tmp during build phase. 

    - This enables reproducible builds by discarding the `__pycache__` directories
  (instead of the current behavior of persisting them in the cpython layer).
- The `__pycache__` directories are not reproducible and are effectively opaque
  to us. We cannot make them reproducible, so discarding them is the only
  option for reproducible builds.
- The PYTHONPYCACHEPREFIX environment variable was chosen to allow users to
  override it if needed, whereas setting PYTHONDONTWRITEBYTECODE=true would
  have been harder, if not impossible, to allow users to override.
- Setting this environment variable as a build environment on the layer
  (v.s. e.g. in process via os.SetEnv()) means all subsequent buildpacks (e.g.
  pip, poetry, etc) will have this environment variable set automatically by
  the lifecycle.
- We only set this environment variable for the build phase (and not the launch
  phase) to allow users to continue to leverage `__pycache__` directories at
  launch time if they wish. The current launch-time behavior of defaulting to
  $HOME/.pycache is unchanged.
- Also update the README to include this new feature and various other minor
  README improvements.
    @robdimsdale
    robdimsdale committed Oct 25, 2022
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  2. Reorder README.

    @robdimsdale
    robdimsdale committed Oct 25, 2022
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