Talks: How We Migrated 3.8 Million Lines of Python 2 Without Interrupting Development

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Migrating from python 2 to python 3 is not very easy, but it can be exacerbated by needing to port a large codebase modified frequently by many different developers. Our codebase was nearly 4 million lines of code modified dozens of times a day by hundreds of total developers. It is also business critical, containing a large portion of our most important code and data. We used several tools, techniques, and patterns to achieve the migration without disrupting day-to-day development and keeping regressions a minimum. In this talk, we’ll detail our migration steps, our usage of pre-commit hooks to reduce regressions to fixes, our usage of a reverse proxy to allow granular, low risk rollout for a webapp, and our migration of pickle to rollforward safe json for caching.