gendalf 0.4.0

A Python codegen tool for transport layers in DDD, supporting most popular transport / API frameworks.

You shall pass... your code to adapters!

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Gendalf is a code-first generator for Python adapters.

It generates type-safe transport and persistence layers directly from existing Python code and SQL files — without requiring OpenAPI, Protobuf, AsyncAPI, or ORMs.

Your code is the source of truth.
Gendalf generates the glue.

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Key ideas

• Code-first

  • Adapters are generated from Python modules and SQL files
  • No external specs to write or maintain

• Deterministic

  • Gendalf uses a deterministic, AST-based algorithm to analyze code and generate adapters
  • It does not use LLMs or any probabilistic generation
  • Given the same inputs, the output is always identical

• Adapter-oriented

  • Transport adapters: FastAPI servers, HTTP clients, gRPC, WebSockets
  • Persistence adapters: SQL → typed Python APIs
  • Boundary code only — business logic remains untouched

• Type-safe

  • Python types propagate across generated code
  • SQL queries produce typed inputs and outputs

• Minimal opt-in

  • Use standard Python type annotations
  • Mark Python classes intended as entrypoints with @entrypoint
  • Add -- sqlcast markers to SQL files
  • Everything else is inferred

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Why Gendalf

Most code generators require you to:

• write specs first,
• duplicate models,
• adopt specific frameworks or ORMs.

LLM-based code generation introduces other problems:

• non-deterministic output,
• mandatory manual review,
• runtime cost and token usage.

Gendalf does the opposite:

• Python code defines the contract,
• SQL defines persistence,
• adapters and DTOs are generated by explicit algorithms (type inspection and AST traversal).

Generated code can be committed, regenerated in CI, and treated as compiler output.

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Transports

FastAPI & HTTPX

Run with gendalf src cast fastapi.

Supported patterns:

• request-response (POST, JSON body)
• duplex streaming (WebSocket, JSON frames)

Generated code

• src/api/fastapi/models.py — Pydantic request/response models
• src/api/fastapi/client.py — async typed HTTP client
• src/api/fastapi/server.py — server handlers with serialization and domain invocation

Generated code is complete and requires no manual edits.

Aiohttp

Run with gendalf src cast aiohttp.

Supported patterns:

• request-response (POST, JSON body)
• duplex streaming (WebSocket, JSON frames)

Generated code

• src/api/aiohttp/models.py
• src/api/aiohttp/client.py
• src/api/aiohttp/server.py

Examples

• my greeter

gRPC (planned)

Not supported yet.

Planned:

• unary-unary
• unary-stream
• stream-unary
• stream-stream

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Persistence

SQL

WIP: Generate type-safe Python APIs directly from SQL files — no ORM required.