Rewrite .NET Framework codebases to Python with parity

If you’re asking “how do I rewrite .NET Framework to Python,” our LEAP Protocol gives a precise, low-risk path: extract specs → generate tests → implement in parallel → roll out with parity. First, we extract an executable spec from your .NET Framework app (ASP.NET MVC/WebForms/WCF/EF) by mapping routes, contracts, data shapes, and side effects. Next, we generate a comprehensive, automated test suite (pytest) from real traffic and fixtures, locking in the current behavior—including edge cases—before any rewrite begins. Then our engineers implement the Python version in parallel (typically FastAPI + SQLAlchemy + Celery), continuously running the spec-driven tests to guarantee equivalence. Finally, we roll out with parity using a strangler-fig pattern: route-by-route cutover behind IIS/NGINX, shadow traffic, and dual-write/compare for critical flows until confidence is proven. The result is a modern, container-friendly Python service with the same observable behavior, backed by tests you own. LEAP is spec-first, test-gated, and agent-agnostic; we use human experts and AI agents under test to accelerate delivery while keeping correctness front and center.

Why Python for .NET Framework migrations

• Cross-platform and container-native: run on Linux with uvicorn/gunicorn behind NGINX, simplifying CI/CD and Kubernetes without Windows Server or IIS lock-in.
• Modern web stack: FastAPI (ASGI) + Pydantic delivers concise, type-validated APIs with excellent async I/O for high-concurrency HTTP and background tasks.
• Rich data and jobs: SQLAlchemy/Alembic for ORM and migrations; Celery/APScheduler for Hangfire/Quartz.NET equivalents; broad ecosystem for scripting and ML add-ons.
• Observability and ops: OpenTelemetry and structlog/loguru integrate cleanly; environment-based configuration with Pydantic Settings replaces web.config transforms.
• Talent and velocity: a large pool of Python developers and libraries reduces time-to-feature for services, data pipelines, and integrations.

Our methodology

1) Spec extraction from .NET
- Inventory ASP.NET MVC/WebForms routes, WCF contracts, EF models, filters (Global.asax), HttpModules/Handlers, and IIS URL Rewrite rules.
- Derive an executable spec: HTTP endpoints, payload schemas, auth flows, DB queries, background jobs, file and registry I/O, and error semantics.

2) Test generation and baselining
- Build pytest suites from recorded requests/responses (golden master), contract tests from WCF/WSDL or Swagger where available, and DB invariants.
- Property and boundary tests (Hypothesis where useful) to lock in edge behavior for model binding, validation, culture/locale, and rounding.

3) Parallel implementation in Python
- Web: FastAPI + Pydantic models; ASGI middleware for auth, correlation, and cross-cutting concerns.
- Data: SQLAlchemy Core/ORM with Alembic; map LINQ queries to SQLAlchemy expressions and preserve EF transaction semantics.
- Jobs: Celery or APScheduler to replace Hangfire/Quartz.NET; idempotent handlers with retry and backoff.
- Interop: libraries for AD/Kerberos (pyspnego/python-ldap), SMTP, S3/Azure Blob, and message queues; optional SOAP compatibility via spyne if needed.

4) Strangler rollout with parity
- Deploy Python alongside the .NET app; reverse-proxy by route or feature.
- Shadow traffic and dual-write with read-compare for critical tables.
- Monitor latencies, error rates, and logs; cut over incrementally once tests and SLOs are green.

5) Handoff and hardening
- Deliver the spec, test suite, Python code, CI/CD, and runbooks.
- Train your team, remove the legacy endpoints, and schedule follow-up for post-cutover refinements.

Specific .NET Framework concerns we handle

• ASP.NET WebForms to stateless APIs: replace ViewState/postbacks and server controls with explicit FastAPI endpoints and Pydantic validators; re-create model binding quirks in tests to avoid surprises.
• WCF/SOAP and binary serializers: convert DataContract/MessageContract services to REST/OpenAPI; if SOAP is required, maintain a SOAP surface via spyne while internal logic runs in Python.
• Entity Framework to SQLAlchemy: translate LINQ-to-Entities, Includes, lazy/eager loading, concurrency tokens (rowversion), and transaction scopes to SQLAlchemy Core/ORM with explicit transactions.
• Windows-only integrations: map NTLM/Kerberos and AD group checks via reverse proxy (Negotiate) or pyspnego; replace Registry/COM/System.Drawing with environment-based config, Python wrappers, or external services (e.g., Pillow/ImageMagick).
• IIS/web.config features: convert URL Rewrite, HttpModules/Handlers, and Global.asax events to ASGI middleware and router policies; migrate config transforms to Pydantic Settings and secrets stores.

Proof

• sqlite-leap — five SQLite engines from one spec: https://github.com/safitudo/sqlite-leap
• semver-leap — 5,632 passing tests validating behavior: https://github.com/safitudo/semver-leap
• LEAP Protocol (spec-first, test-gated, agent-agnostic): https://github.com/safitudo/leap

Pricing & timeline

• Typical engagement: 4–12 weeks depending on scope and integrations.
• Fixed-price proposal after a 1–2 week discovery/spec phase.
• Most projects land between $40k and $120k, including the executable spec, full pytest suite, Python implementation (FastAPI/SQLAlchemy/Celery), CI/CD, and a staged cutover plan.

Ready to modernize your .NET Framework system with measurable, test-proven parity? Request a scoped assessment and we’ll return a fixed plan, timeline, and price grounded in your code and traffic.

Leap Agentic is distinct from Legacyleap.ai and Impetus Leap AI.

Leap Agentic is distinct from Legacyleap.ai and Impetus Leap AI.