emend 0.1.0

A Python refactoring CLI tool with structured edits and pattern transforms

emend

A Python refactoring CLI tool built on LibCST, with AST-based commands for handling nested functions and closures.

Built on two complementary systems:

• Structured Edits - Precise changes to symbol metadata using selectors like file.py::func[params][0]
• Pattern Transforms - Code-pattern search and replace with capture variables like print($X) → logger.info($X)

Installation

Using uv (recommended)

uv tool install emend

Using pip

pip install emend

Verify the installation:

emend --help

Usage

emend <command> [options]

Workflow

1. Preview changes: Run with --dry-run (default) to see what will change
2. Review the diff output
3. Apply changes: Re-run with --apply
4. Format code: Run formatters (black/ruff/isort) - emend may not preserve exact formatting
5. Verify: Run tests/type checks

Selector Syntax

Three types of selectors:

Symbol Selectors

file.py::Class.method.nested   # Nested symbol path
file.py::func                  # Module-level symbol

Extended Selectors (with components)

file.py::func[params]           # Function parameters
file.py::func[params][ctx]      # Specific parameter (by name)
file.py::func[params][0]        # Specific parameter (by index)
file.py::func[returns]          # Return annotation
file.py::func[decorators]       # Decorator list
file.py::MyClass[bases]         # Base classes
file.py::func[body]             # Function body

Pseudo-class Selectors

file.py::func[params]:KEYWORD_ONLY       # Keyword-only parameter slot
file.py::func[params]:POSITIONAL_ONLY    # Positional-only parameter slot

Line Selectors

file.py:42                      # Single line
file.py:42-100                  # Line range

Wildcard Selectors

file.py::*[params]              # All function parameters
file.py::Test*[decorators]      # Test class parameters
file.py::*.*[returns]           # All method return types
file.py::Class.*[body]          # All method bodies in Class

Wildcards support glob patterns:

• * - Match any symbol at this level
• Test* - Match symbols starting with Test
• *.* - Match any method in any class
• Class.* - Match any method in Class

Selector Grammar (Lark)

start: selector

selector: file_path DOUBLE_COLON symbol_path? component*

file_path: PATH
symbol_path: IDENTIFIER ("." IDENTIFIER)*
component: "[" COMPONENT_NAME "]" accessor? pseudo_class?
accessor: "[" (IDENTIFIER | INT) "]"
pseudo_class: PSEUDO_CLASS

COMPONENT_NAME: "params" | "returns" | "decorators" | "bases" | "body" | "imports"
DOUBLE_COLON: "::"
PATH: /[^:]+/
IDENTIFIER: /[a-zA-Z_][a-zA-Z0-9_]*/
INT: /\d+/
PSEUDO_CLASS: /:KEYWORD_ONLY|:POSITIONAL_ONLY|:POSITIONAL_OR_KEYWORD/

Commands

Search & Read

search - Unified search with auto-detection

• Pattern mode: emend search 'print($X)' file.py
• Lookup mode: emend search file.py::func
• Summary mode: emend search file.py (list symbols)
• Filters: --kind, --name, --returns, --depth, --has-param, --output, --where, --imported-from, --scope-local
• Output formats: code, location, selector, summary, metadata, json, count, summary::flat, code::dedent
• Also available as: query, show, get, lookup, find for intuitive workflows

Edit & Transform

edit - Modify or remove existing symbol components

• Replace: emend edit file.py::func[returns] "int" --apply
• Insert: emend edit file.py::func[params] "new_param" --before ctx --apply
• Remove: emend edit file.py::func[params][old_param] --rm --apply
• Wildcards: emend edit 'file.py::*[decorators]' "@dataclass" --apply

add - Insert new items into list components (alternative to edit)

• emend add file.py::func[params] "timeout: int = 30" --apply
• emend add "file.py::func[params]:KEYWORD_ONLY" "debug: bool" --apply

replace - Replace pattern matches with pattern-based substitution

• emend replace 'print($X)' 'logger.info($X)' file.py --apply
• Scope constraints: --in, --inside, --not-inside, --where

Symbol Management

refs - Find all references to a symbol across the project

• emend refs models.py::User
• Filters: --writes-only, --reads-only, --calls-only
• Output: --output json, --output location

rename - Rename a symbol or module across the project

• Symbol: emend rename models.py::User --to Account --apply
• Module: emend rename models.py --to accounts.py --apply
• Filters: --docs, --no-hierarchy, --unsure

move - Move a symbol or module with automatic import updates

• Symbol: emend move utils.py::parse_date helpers/dates.py --apply
• Module: emend move utils.py helpers/utils.py --apply

copy-to - Copy a symbol to another file

• emend copy-to workflow.py::Builder._build.helper tasks.py --dedent --apply

Utilities

batch - Apply multiple refactoring operations from YAML/JSON file

• emend batch rules.json --apply

lint - Lint files using pattern rules from .emend/patterns.yaml

• emend lint src/
• emend lint src/ --fix --apply to auto-fix issues

graph - Generate a call graph for functions in a file

• emend graph src/module.py --format plain
• Formats: plain, json, dot

Examples

Search & Read Examples

# Search by pattern (pattern mode)
emend search 'print($X)' src/
emend search 'assertEqual($A, $B)' tests/ --output count

# Search by symbol (lookup mode)
emend search file.py::func
emend search src/ --kind function --name test_*
emend search file.py --output json

# Extract function parameters
emend search api.py::handler[params]
emend search 'api.py::*[params]'  # Wildcard: all function params in file

# Get return types
emend search 'src/**/*.py::*[returns]' --output metadata

# List symbols in a module
emend search file.py                          # Tree view
emend search file.py --output summary::flat   # Flat list
emend search file.py --depth 2                # Limit nesting depth

Edit Examples

# Update return type
emend edit api.py::handler[returns] "Response" --apply

# Add parameter with default value
emend edit api.py::handler[params] "timeout: int = 30" --apply

# Add keyword-only parameter
emend edit "api.py::handler[params]:KEYWORD_ONLY" "debug: bool" --apply

# Insert parameter before specific param
emend edit api.py::handler[params] "ctx: Context" --before user_id --apply

# Remove a specific parameter
emend edit api.py::handler[params][deprecated_arg] --rm --apply

# Edit multiple symbols at once (wildcards)
emend edit 'file.py::*[decorators]' "@dataclass" --apply

Pattern Transform Examples

# Simple find and replace (dry-run by default)
emend replace 'print($X)' 'logger.info($X)' file.py

# Replace within a specific scope
emend replace 'old_var' 'new_var' api.py --in process --apply

# Replace with pattern capture
emend replace 'get_field($N)' 'field$N' api.py --in process --apply

# Find all pattern matches
emend search 'print($X)' src/ --output location

# Multi-rule batch operations
emend batch rules.json --apply

Symbol Management Examples

# Find all references to a symbol
emend refs models.py::User --output json
emend refs models.py::User --writes-only    # Only write references
emend refs models.py::User --calls-only     # Only function calls

# Rename a symbol project-wide
emend rename models.py::User --to Account --apply

# Move a symbol to another file (updates imports)
emend move utils.py::parse_date helpers/dates.py --apply

# Copy a symbol to another file
emend copy-to workflow.py::Builder._build.helper tasks.py --dedent --apply

# List symbols using search
emend search workflow.py --depth 3

Pattern Syntax

Patterns support metavariables for capturing:

# Single expression
emend find 'print($MSG)' src/

# Multiple arguments with capture
emend find 'func($A, $B)' src/

# Variable arguments
emend find 'func($...ARGS)' src/

# Type constraints
emend find 'range($N:int)' src/

# Anonymous metavariables
emend find 'func($_, $ARG)' src/

# Structural constraints
emend find 'print($X)' src/ --inside 'async def'
emend find 'await $X' src/ --not-inside 'if __debug__'

# Supported pattern types:
#   Literals: $X, $MSG:str, $N:int, 3.14
#   Calls: func($X), obj.method($A, $B)
#   Operations: $A + $B, $A and $B, not $X, $X[$Y]
#   Collections: ($A, $B), [$X, $Y], {$K: $V}
#   Control: return $X, assert $A == $B, raise $EXC

Pattern Grammar (Lark)

start: pattern

pattern: (code_chunk | metavar)+

metavar: DOLLAR (ELLIPSIS)? METAVAR_NAME TYPE_CONSTRAINT?
       | DOLLAR UNDERSCORE

DOLLAR: "$"
ELLIPSIS: "..."
UNDERSCORE: "_"
METAVAR_NAME: /[A-Z][A-Z0-9_]*/
TYPE_CONSTRAINT: /:(?:expr|stmt|identifier|int|str|float|call|attr|any)/
code_chunk: /[^$:]+/ | ":"

The code_chunk rule excludes colons (/[^$:]+/) to prevent consuming colons that are part of type constraints (e.g., $MSG:str). A standalone colon is matched by the alternative | ":" for patterns containing colons outside of type constraints.

Diff Patch Format

- pattern_to_find
+ replacement_pattern

- another_pattern
+ another_replacement

Lines prefixed with - are matched; corresponding + lines are the replacement. Blank lines separate rules.

Development

Installing from Source

Clone the repository and install for development:

git clone https://github.com/anthropics/emend
cd emend

# Using make (creates virtual environment)
make venv

# Or manually:
python3 -m venv .venv
.venv/bin/pip install -e ".[dev]"

Running Tests

# Run all tests
make test

# Run specific test file
make test TESTS=tests/test_emend/test_add_parameter.py

# Run specific test
make test TESTS="tests/test_emend/test_add_parameter.py::test_add_parameter_with_default"

Project Structure

emend/
├── src/emend/
│   ├── cli.py                # CLI entry point, argument parsing
│   ├── transform.py          # Transform primitives (get/set/add/remove/find/replace)
│   ├── pattern.py            # Pattern parsing and compilation
│   ├── query.py              # Symbol querying with filters
│   ├── ast_commands.py       # AST-based command implementations
│   ├── ast_utils.py          # AST traversal utilities
│   ├── component_selector.py # Extended selector parsing
│   └── grammars/
│       ├── selector.lark     # Extended selector grammar
│       └── pattern.lark      # Pattern grammar
├── tests/test_emend/         # Test suite
├── Makefile
└── pyproject.toml

License

MPL 2.0