Documentation on reducing package size and custom CFLAGS

[peterroelants]

Change Summary

• Documentation update on how to custom compile pydantic when using pip install.
• Small change in setup.py to allow for custom CFLAGS when compiling.

Setup.py CFLAGS

pydantic's setup.py overwrites all custom CFLAGS that a user might pass in when rebuilding pydantic.
This change appends custom CFLAGS to the current CFLAGS used when building. There should not be any change in the current default behaviour.

By appending custom CFLAGS to the end it is possible to overwrite the default optimization flags currently used in pydantic. From the gcc docs:

If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.

Performance impact of setting different CFLAGS

	size	benchmark avg time
default pip install (from PyPI)	45M	70.7μs
pip install --no-binary (from PyPI)	796K	101.4μs
pip install --no-binary (from PyPI) with cython	6.4M	67.8μs
pip install --no-binary with cython CFLAG "-O3" (This branch)	6.4M	68.1μs
pip install --no-binary with cython CFLAG "-Os" (This branch)	5.2M	74.6μs

Related issue number

Issue #2276 will be resolved by documenting how to reduce pydantic installation size. Additionally, users can pass in custom CFLAGs to trade-off speed vs size.

Checklist

• Unit tests for the changes exist (Already existent)
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)

[codecov]

Codecov Report

Merging #2517 (a2efe5b) into master (7b7e705) will not change coverage.
The diff coverage is n/a.

❗ Current head a2efe5b differs from pull request most recent head d755928. Consider uploading reports for the commit d755928 to get more accurate results

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##            master     #2517   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           25        25           
  Lines         5109      5109           
  Branches      1050      1050           
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  Hits          5109      5109           

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[peterroelants]

@PrettyWood I was wondering, should I request a review for this somewhere? And if so, where can I do this?
Or should I just leave it to be reviewed eventually?

[PrettyWood]

I let Samuel merge PRs. Nothing to do on your side ;)

[samuelcolvin]

Hopefully I can make time to work on pydantic next week.

[peterroelants]

Great, I'll leave it here then. No rush from my side.

[samuelcolvin]

otherwise LGTM.

[samuelcolvin]

👍

[samuelcolvin]

please update.

[peterroelants]

please update.

@samuelcolvin Thank you for the review. I updated this PR according to the suggestions, rebased the changes on the latest master, and pushed the changes here. This should be ready to merge. please review.

[PrettyWood]

Please update and rebase/merge to have new deps to fix CI.
Otherwise looks good thanks!

[peterroelants]

@PrettyWood I:

• Merged your suggestion,
• Squashed the commits into a single commit while rebasing on the latest master,
• Pushed changes to this branch.

Please review

[PrettyWood]

https://smokeshow.helpmanual.io/4944455v3p5m500e732e/install/

I think you need to remove the colon at the end of !!! note:
Please update

[peterroelants]

https://smokeshow.helpmanual.io/4944455v3p5m500e732e/install/

I think you need to remove the colon at the end of !!! note:
Please update

resolved

please review