Show HN: Codegen – OSS Python Library for Advanced Code Manipulation

Hey HN! We've just open-sourced Codegen (https://github.com/codegen-sh/codegen-sdk), a Python library for manipulating Python + JS/React codebases.

Codegen was engineered backwards from real-world, large-scale codebase analysis + refactors we performed on multi-million-line enterprise codebases. It provides a scriptable interface to a powerful, multi-lingual language server built on Tree-sitter.

We realized that many code transformation tasks that impact large teams - refactors, enforcing patterns, analyzing control flow - are fundamentally programmatic operations. Yet existing tools like LibCST and Jscodeshift often require you to think in terms of ASTs and parser internals rather than the high-level changes you want to make.

Therefore, we built Codegen to match how developers actually think about code changes:

  # Move a symbol to a new file
  # Handles imports, references, dependencies
  function.move_to_file("new_file.py") 

  # Rename across the codebase
  class_def.rename("NewName")  # Updates all usages, preserves formatting

  # Analyze call patterns
  for usage in function.usages:
      print(f"Used in {usage.file.name}")

Codegen handles the edge cases automatically - updating imports, preserving dependencies, maintaining references, and resolving naming conflicts. You focus on intent, we handle the details.

Under the hood, Codegen performs static analysis to build a rich graph representation of your code. This enables:

- Versatile and comprehensive operations

- Built-in visualization capabilities

- Blazing fast execution of large-scale refactors

We've seen a wide variety of advanced code manipulation programs emerge, including:

- Mining codebases for LLM pre-training data

- Analyzing security vulnerabilities

- Large-scale API migrations

- Enforcing code patterns

We're excited to share this with the community and look forward to your feedback. Give it a spin and let us know what you think!

  uv tool install codegen
  codegen notebook --demo

Docs: https://docs.codegen.com GitHub: https://github.com/codegen-sh/codegen-sdk Community: https://community.codegen.com

Let us know if you have any questions or interesting use cases you'd like to explore.