Python 2 to 3 Program Playbook

Migrate remaining Python 2 codebases to Python 3 as a coordinated program. Raise test coverage first, automate conversion, then modernize idioms and add type hints before cutting over.

Difficulty

Intermediate

Phases

Total Duration

20 weeks

Roles

Python 2 reached end of life years ago, yet long-lived backend systems still run it. This program migrates those codebases to Python 3, treating the move as a chance to modernize idioms and add type safety rather than a mechanical port. Strong test coverage is the foundation that makes the migration safe.

Phase-by-Phase

Inventory and Test Coverage. Catalog every Python 2 codebase and its third-party dependencies, flagging packages with no Python 3 release. Raise test coverage to a level where behavior changes will be detected; the migration is only as safe as the tests that guard it.

Automated Conversion. Run automated 2to3 conversion as a starting point, then fix what tooling cannot: the str/bytes split, integer division, dictionary view changes, and removed standard-library modules. A CI gate blocks Python 2 syntax from re-entering the codebase.

Modernization and Typing. Add type hints, adopt f-strings, dataclasses, and context managers, and upgrade dependencies to current versions. Static analysis in CI catches type and security issues introduced during the rewrite.

Cutover and Cleanup. Remove __future__ imports and six-style compatibility shims, cut over runtimes with a canary rollout, and decommission Python 2 interpreters. The program ends when no Python 2 remains in build or runtime.

Team and Roles

An architect sets typing and dependency standards. Backend engineers do the conversion and modernization. QA owns the coverage baseline and regression validation. DevOps maintains the CI gate and runtime cutover.

Risks and Mitigations

The str/bytes distinction is the classic source of silent bugs; targeted tests around encoding boundaries catch them. Unmaintained dependencies may force replacement or vendoring, identified in the audit. Silent behavior changes (division, ordering) are caught by the coverage raised in phase one. Coordinate shared-library upgrades so apps migrate against a stable base.

Success Criteria

Success is high test coverage, current dependencies, improved deployment frequency, and better MTTR. No Python 2 interpreter should remain in production or CI.

Tooling

Use automated conversion tooling as a first pass, type checkers and linters in CI, Docker for runtime parity, and a Git-driven pipeline. Frameworks such as Django or FastAPI host the modernized services.

See a real scan run

A replay of the actual CLI running against our test repositories — live progress, real findings, a genuine DriftScore. Nothing executes in your browser.

Replay

demo@vibgrate — bash

❯ npx @vibgrate/cli scan

╭──────────────────────────────────────────╮

│ Vibgrate Drift Report │

╰──────────────────────────────────────────╯

── node-turborepo (node) .

Runtime: >=18.0.0 (6 majors behind)

Frameworks:

Turbo: 1.13.4 → 2.10.12 (1 behind)

TypeScript: 5.9.3 → 7.0.2 (2 behind)

Dependencies:

1 current 1 1-behind 3 2+ behind 1 unknown

── @repo/admin (node) apps/admin

Frameworks:

TanStack Query: 5.102.5 → 5.102.5 (current)

React: 18.3.1 → 19.2.8 (1 behind)

React DOM: 18.3.1 → 19.2.8 (1 behind)

TypeScript: 5.9.3 → 7.0.2 (2 behind)

Vite: 5.4.21 → 8.2.2 (3 behind)

Dependencies:

3 current 9 1-behind 3 2+ behind 4 unknown

── @repo/api (node) apps/api

Frameworks:

Express: 4.22.2 → 5.2.1 (1 behind)

TypeScript: 5.9.3 → 7.0.2 (2 behind)

Vitest: 1.6.1 → 4.1.11 (3 behind)

Dependencies:

7 current 5 1-behind 3 2+ behind 4 unknown

── @repo/web (node) apps/web

Frameworks:

Next.js: 14.2.35 → 16.3.3 (2 behind)

React: 18.3.1 → 19.2.8 (1 behind)

React DOM: 18.3.1 → 19.2.8 (1 behind)

TypeScript: 5.9.3 → 7.0.2 (2 behind)

Dependencies:

2 current 6 1-behind 3 2+ behind 5 unknown

── @repo/config (node) packages/config

Frameworks:

TypeScript: 5.9.3 → 7.0.2 (2 behind)

Dependencies:

2 current 2 1-behind 5 2+ behind 0 unknown

── @repo/database (node) packages/database

Frameworks:

Prisma: 5.22.0 → 7.10.0 (2 behind)

TypeScript: 5.9.3 → 7.0.2 (2 behind)

Dependencies:

1 current 0 1-behind 3 2+ behind 1 unknown

── @repo/types (node) packages/types

Frameworks:

TypeScript: 5.9.3 → 7.0.2 (2 behind)

Dependencies:

0 current 0 1-behind 1 2+ behind 1 unknown

── @repo/ui (node) packages/ui

Frameworks:

React: 18.3.1 → 19.2.8 (1 behind)

TypeScript: 5.9.3 → 7.0.2 (2 behind)

React: 18.3.1 → 19.2.8 (1 behind)

Dependencies:

1 current 4 1-behind 1 2+ behind 1 unknown

── @repo/utils (node) packages/utils

Frameworks:

TypeScript: 5.9.3 → 7.0.2 (2 behind)

Vitest: 1.6.1 → 4.1.11 (3 behind)

Dependencies:

0 current 1 1-behind 2 2+ behind 1 unknown

Tech Stack

Frontend: React, React DOM

Meta-frameworks: Next.js

Bundlers: tsx, Turbo, Vite

CSS / UI: Autoprefixer, PostCSS, Tailwind CSS

Backend: Express

ORM / Database: Prisma, Prisma Client

Testing: Vitest

Lint & Format: ESLint, ESLint Prettier, ESLint React, Prettier, typescript-eslint

Services & Integrations

Auth: JWT 9.0.3

Databases: Prisma 5.22.0

TypeScript

v5.3.3 · strict ✔ · MIXED · target: ES2022

Build & Deploy

Package Managers: pnpm

Monorepo: npm-workspaces, pnpm-workspaces, turbo

Product Purpose Signals

Frameworks: react, nextjs

Evidence: 177

Top Signals:

- [heading] Dashboard (apps/admin/src/pages/Dashboard.tsx)

- [title] Revenue Overview (apps/admin/src/pages/Dashboard.tsx)

- [copy] workspace:* (packages/ui/package.json)

- [copy] ./dist (packages/ui/tsconfig.json)

- [copy] ./src/index.ts (packages/ui/package.json)

- [copy] @repo/config/tsconfig-base.json (packages/ui/tsconfig.json)

- [copy] @repo/ui (packages/ui/package.json)

- [copy] #3b82f6 (apps/admin/src/pages/Dashboard.tsx)

Unknowns:

- No pricing or billing evidence found.

- No integrations/connectors evidence found.

- No route structure evidence found.

Security Posture

Lockfile ✖ · .env ✔ · node_modules ✔

Platform

Native modules: turbo

Code Quality

Files: 36 · Functions: 183 · Avg complexity: 2.62 · Avg length: 21.13 lines

Max nesting: 2 · Circular deps: 0 · Dead code: 0%

God files: apps/admin/src/pages/Products (448 lines)

Database Schema

postgresql · 8 models · 1 enum

Models: Address, CartItem, Category, Order, OrderItem (+3 more)

Findings (16 errors, 11 warnings)

✖ Node.js runtime ">=18.0.0" reached end-of-life on 2025-04-30 (latest: 24.0.0).

vibgrate/runtime-eol in .

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in .

✖ 60% of dependencies are 2+ major versions behind in node-turborepo.

vibgrate/dependency-rot in .

✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).

vibgrate/dependency-major-lag in .

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in apps/admin

✖ Vite is 3 major versions behind (current: 5.4.21, latest: 8.2.2).

vibgrate/framework-major-lag in apps/admin

✖ vite is 3 major versions behind (spec: ^5.0.12, latest: 8.2.2).

vibgrate/dependency-major-lag in apps/admin

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in apps/api

✖ Vitest is 3 major versions behind (current: 1.6.1, latest: 4.1.11).

vibgrate/framework-major-lag in apps/api

✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).

vibgrate/dependency-major-lag in apps/api

✖ vitest is 3 major versions behind (spec: ^1.2.1, latest: 4.1.11).

vibgrate/dependency-major-lag in apps/api

⚠ Next.js is 2 major versions behind (current: 14.2.35, latest: 16.3.3).

vibgrate/framework-major-lag in apps/web

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in apps/web

✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).

vibgrate/dependency-major-lag in apps/web

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in packages/config

✖ 56% of dependencies are 2+ major versions behind in @repo/config.

vibgrate/dependency-rot in packages/config

✖ eslint-plugin-react-hooks is 3 major versions behind (spec: ^4.6.0, latest: 7.1.1).

vibgrate/dependency-major-lag in packages/config

⚠ Prisma is 2 major versions behind (current: 5.22.0, latest: 7.10.0).

vibgrate/framework-major-lag in packages/database

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in packages/database

✖ 75% of dependencies are 2+ major versions behind in @repo/database.

vibgrate/dependency-rot in packages/database

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in packages/types

✖ 100% of dependencies are 2+ major versions behind in @repo/types.

vibgrate/dependency-rot in packages/types

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in packages/ui

⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).

vibgrate/framework-major-lag in packages/utils

✖ Vitest is 3 major versions behind (current: 1.6.1, latest: 4.1.11).

vibgrate/framework-major-lag in packages/utils

✖ 67% of dependencies are 2+ major versions behind in @repo/utils.

vibgrate/dependency-rot in packages/utils

✖ vitest is 3 major versions behind (spec: ^1.2.1, latest: 4.1.11).

vibgrate/dependency-major-lag in packages/utils

╭──────────────────────────────────────────╮

│ Top Priority Actions │

╰──────────────────────────────────────────╯

1. Upgrade EOL runtime in node-turborepo

End-of-life runtimes no longer receive security patches and block ecosystem upgrades.

./.

>=18.0.0 → 24.0.0 (6 majors behind)

Impact: −10 drift points (runtime & EOL)

2. Fix security posture: no lockfile found

Without a lockfile, installs are non-deterministic. Run the install command to generate one and commit it.

Missing: package-lock.json, pnpm-lock.yaml, or yarn.lock

3. Upgrade Vite 5.4.21 → 8.2.2 in @repo/admin (+2 more)

3 major versions behind. Major framework drift increases breaking change risk and blocks access to security fixes and performance improvements.

./apps/admin

Vite: 5.4.21 → 8.2.2 (3 majors behind)

./apps/api

Vitest: 1.6.1 → 4.1.11 (3 majors behind)

./packages/utils

Vitest: 1.6.1 → 4.1.11 (3 majors behind)

Impact: −5–15 drift points

4. Reduce dependency rot in @repo/types (100% severely outdated)

1 of 1 dependencies are 2+ majors behind. Run `npm outdated` and prioritise packages with known CVEs or breaking API changes.

./packages/types

typescript: 5.9.3 → 7.0.2 (2 majors behind)

Impact: −5–10 drift points

5. Reduce dependency rot in @repo/database (75% severely outdated)

3 of 4 dependencies are 2+ majors behind. Run `npm outdated` and prioritise packages with known CVEs or breaking API changes.

./packages/database

@prisma/client: 5.22.0 → 7.10.0 (2 majors behind)

prisma: 5.22.0 → 7.10.0 (2 majors behind)

typescript: 5.9.3 → 7.0.2 (2 majors behind)

Impact: −5–10 drift points

╭──────────────────────────────────────────╮

│ Architecture Layers │

╰──────────────────────────────────────────╯

Archetype: nextjs (80% confidence)

Files classified: 24 (11 unclassified)

Folders classified: 8

apps/admin/src presentation 100% 4 files

apps/admin/src/pages presentation 100% 2 files

apps/api/src/middleware middleware 100% 2 files

apps/api/src/routes routing 100% 2 files

apps/web/src/app presentation 100% 4 files

apps/web/src/app/products presentation 100% 2 files

apps/web/src/app/products/[id] presentation 100% 1 file

packages/ui/src presentation 100% 6 files

Unclassified source (sample): 11

presentation 15 files drift ████████████████████ 100 risk high

routing 4 files drift ████████████████████ 100 risk high

middleware 2 files drift ███████▍░░░░░░░░░░░░ 37 risk moderate

config 2 files drift ░░░░░░░░░░░░░░░░░░░░ 0 risk none

shared 1 file drift ████████████████████ 100 risk high

╭──────────────────────────────────────────╮

│ DriftScore Summary │

╰──────────────────────────────────────────╯

DriftScore: 66/100

Risk Level: HIGH

Projects: 9

Classified: 8 nano · 1 micro · 0 small · 0 standard

Billable: 0.42 · 9 detected → 0.42 billable projects (micro-project pricing)

0.1 micro · 0.32 nano

These fractions add up across repositories, then round down to whole billable projects.

Score Breakdown

Runtime: ████████████████████ 100

Frameworks: █████████▏░░░░░░░░░░ 46

Dependencies: ██████▏░░░░░░░░░░░░░ 31

EOL Risk: ████████████████████ 100

Scanned at 2026-08-26T09:08:28.481Z · 7.1s · 286 files scanned · 56 workspace files · 27 dirs

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Explore the Vibgrate CLI

Python 2 to 3 Program Playbook

Phase-by-Phase

Team and Roles

Risks and Mitigations

Success Criteria

Tooling

Category

Tags

See a real scan run