Guiding Principles

Codegen was developed by working backwards from real-world, large-scale codebase migrations. Instead of starting with abstract syntax trees and parser theory, we started with the question: “How do developers actually think about code changes?”

This practical origin led to four core principles that shape Codegen’s design:

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Intuitive APIs

Write code that reads like natural language, without worrying about abstract syntax trees or parser internals. Codegen provides high-level APIs that map directly to the transformations developers want to perform:

# Methods that read like English
function.rename("new_name")  # Not ast.update_node(function_node, "name", "new_name")
function.move_to_file("new_file.py")  # Not ast.relocate_node(function_node, "new_file.py")

# Clean, readable properties
if function.is_async:  # Not ast.get_node_attribute(function_node, "async")
    print(function.name)  # Not ast.get_node_name(function_node)

# Natural iteration patterns
for usage in function.usages:  # Not ast.find_references(function_node)
    print(f"Used in {usage.file.name}")

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No Sharp Edges

Focus on your high-level intent while Codegen handles the intricate details.

Codegen operations handle the edge cases - it should be hard to break lint.

# Moving a function? Codegen handles:
function.move_to_file("new_file.py")
# ✓ Updating all import statements
# ✓ Preserving dependencies
# ✓ Maintaining references
# ✓ Fixing relative imports
# ✓ Resolving naming conflicts

# Renaming a symbol? Codegen manages:
class_def.rename("NewName")
# ✓ Updating all usages
# ✓ Handling string references
# ✓ Preserving docstrings
# ✓ Maintaining inheritance

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Performance through Pre-Computation

Codegen frontloads as much as possible to enable fast, efficient transformations.

It is built with the insight that each codebase only needs to be parsed once per commit.

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Python-First Composability

Codegen embraces Python’s strength as a “glue language” - its ability to seamlessly integrate different tools and APIs. This makes it natural to compose Codegen with your existing toolchain:

• Build complex transforms by combining simpler operations
• Integrate Codegen with your existing tools (linters, type checkers, test frameworks, AI tools)