python-rope-refactoring

Python Rope Refactoring

This skill provides comprehensive guidance on using the rope library for advanced Python refactoring operations.

About Rope

Rope is the world's most advanced open source Python refactoring library. It provides:

• Powerful and safe refactorings: Rename, extract, inline, move, restructure, and more
• Static Object Analysis (SOA): Sophisticated type inference for accurate refactorings
• Cross-project refactorings: Refactor across multiple related projects
• IDE helpers: Auto-completion, find occurrences, definition location
• VCS integration: Git, Mercurial, SVN support

Rope is pure Python with no dependencies, making it ideal for programmatic refactoring.

When to Use This Skill

Use this skill when:

• Performing systematic refactorings across a Python codebase
• Renaming variables, functions, classes, or modules safely
• Extracting methods or variables from complex functions
• Moving code between modules or packages
• Inlining functions or variables
• Restructuring code patterns programmatically
• Need automated, safe refactoring that updates all references

Installation

Install rope using pip:

pip install rope

Core Concepts

Project

A rope Project represents a Python codebase in a directory. All refactorings operate within a project context:

from rope.base.project import Project

# Create a project for the current directory
project = Project('.')

# Or specify a path
project = Project('/path/to/myproject')

# Always close when done
project.close()

Key points about projects:

• A project is a directory that can contain any files
• Rope searches for Python modules/packages inside the project
• Refactorings only change files inside the project
• External modules are analyzed but never modified
• Rope creates a .ropeproject folder for configuration and caching (can be disabled with ropefolder=None)

Resources

Files and folders in rope are accessed through Resource objects (File and Folder):

from rope.base import libutils

# Get a resource for an existing file
resource = libutils.path_to_resource(project, '/path/to/file.py')

# Create a resource for a file that doesn't exist yet
new_file = libutils.path_to_resource(project, '/path/to/new_file.py', type='file')

Changes

Refactorings return Change objects that describe the modifications:

# Get changes from a refactoring
changes = refactoring.get_changes('new_name')

# Preview changes
print(changes.get_description())

# Apply changes
project.do(changes)

# Undo if needed
project.history.undo()

Refactoring Operations

Rename

Rename variables, functions, classes, modules - rope updates all references:

from rope.refactor.rename import Rename

# Get the resource
resource = libutils.path_to_resource(project, 'mymodule.py')

# Create renamer at offset (character position in file)
renamer = Rename(project, resource, offset)

# Get changes with new name
changes = renamer.get_changes('new_name')

# Option: rename in docs/comments too
changes = renamer.get_changes('new_name', docs=True)

# Apply
project.do(changes)

Calculating offsets: Offsets are character positions in the file (0-indexed). DOS line-endings and multi-byte characters count as one character. To find the offset of a name, read the file and use source.find('name') or calculate from line/column positions.

Extract Method

Extract selected code into a new method:

from rope.refactor.extract import ExtractMethod

resource = libutils.path_to_resource(project, 'mymodule.py')

# start and end are character offsets of the region to extract
extractor = ExtractMethod(project, resource, start, end)

# Extract to a method named 'extracted_method'
changes = extractor.get_changes('extracted_method')
project.do(changes)

Options:

• global_: Extract as a global function instead of method
• similar: Extract similar code blocks too

Extract Variable

Extract an expression into a variable:

from rope.refactor.extract import ExtractVariable

resource = libutils.path_to_resource(project, 'mymodule.py')
extractor = ExtractVariable(project, resource, start, end)

changes = extractor.get_changes('extracted_var')
project.do(changes)

Options:

• similar: Extract similar expressions too
• global_: Extract as a global variable

Inline

Inline a method, variable, or parameter (replace uses with the actual value):

from rope.refactor.inline import (
    InlineMethod,
    InlineVariable,
    InlineParameter
)

resource = libutils.path_to_resource(project, 'mymodule.py')

# Inline method
inliner = InlineMethod(project, resource, offset)
changes = inliner.get_changes()
project.do(changes)

# Inline variable
inliner = InlineVariable(project, resource, offset)
changes = inliner.get_changes()
project.do(changes)

Options:

• only_current: Only inline the current occurrence
• remove: Remove the definition after inlining

Move

Move classes, functions, modules, or methods:

from rope.refactor.move import create_move

resource = libutils.path_to_resource(project, 'mymodule.py')

# create_move auto-detects what to move based on offset
mover = create_move(project, resource, offset)

# Move to destination resource (module or package)
dest_resource = libutils.path_to_resource(project, 'newmodule.py')
changes = mover.get_changes(dest_resource)
project.do(changes)

Change Signature

Modify function/method signatures (add, remove, reorder parameters):

from rope.refactor.change_signature import ChangeSignature

resource = libutils.path_to_resource(project, 'mymodule.py')
changer = ChangeSignature(project, resource, offset)

# Get current signature info
signature = changer.get_signature()

# Modify signature - add parameter, remove parameter, reorder, etc.
# See rope documentation for ArgumentReordering and ArgumentAdder
changes = changer.get_changes(new_signature)
project.do(changes)

Restructure

Pattern-based code transformation - the most powerful refactoring:

from rope.refactor.restructure import Restructure

# Pattern: what to match (uses ${} for wildcards)
pattern = '${pow_func}(${param1}, ${param2})'

# Goal: what to replace it with
goal = '${param1} ** ${param2}'

# Args: constraints on wildcards
args = {'pow_func': 'name=mymodule.pow'}

restructuring = Restructure(project, pattern, goal, args)
changes = restructuring.get_changes()
project.do(changes)

Pattern syntax:

• ${name} - wildcard matching any expression
• Constraints: name=module.func, type=mymodule.MyClass, etc.

Common use cases:

• Convert function calls to operators
• Modernize old API calls
• Apply design pattern transformations

Other Refactorings

# Introduce factory
from rope.refactor.introduce_factory import IntroduceFactory

# Encapsulate field (add getter/setter)
from rope.refactor.encapsulate_field import EncapsulateField

# Method to method object
from rope.refactor.method_object import MethodObject

# Local variable to field
from rope.refactor.localtofield import LocalToField

# Module to package
from rope.refactor.topackage import ModuleToPackage

# Organize imports
from rope.refactor.importutils import ImportOrganizer

Best Practices

1. Always Validate Before Refactoring

When files change outside rope, validate to clear caches:

# Validate the entire project
project.validate(project.root)

# Or validate a specific resource
project.validate(resource)

Call this before each refactoring operation when using rope in an IDE or when files may have changed externally.

2. Use Static Object Analysis for Better Results

Run SOA to improve rope's type inference:

from rope.base import libutils

# Analyze a single module
libutils.analyze_module(project, resource)

# Analyze all modules (can be slow on large projects)
libutils.analyze_modules(project)

Run this periodically, especially before large refactorings. SOA analyzes function calls and assignments to infer types.

3. Preview Before Applying

Always preview changes before applying:

changes = refactoring.get_changes('new_name')

# Get description
print(changes.get_description())

# Or inspect the Change object directly for detailed info
for change_set in changes.changes:
    print(change_set.get_description())

# Apply only if satisfied
project.do(changes)

4. Handle Task Progress

For long-running refactorings, use TaskHandle to monitor progress and allow cancellation:

from rope.base.taskhandle import TaskHandle

handle = TaskHandle("Rename refactoring")

def update_progress():
    jobset = handle.current_jobset()
    if jobset:
        percent = jobset.get_percent_done()
        print(f"Progress: {percent}%")

handle.add_observer(update_progress)

# Pass as keyword argument
changes = renamer.get_changes('new_name', task_handle=handle)

5. Close Projects

Always close projects to flush caches and save state:

try:
    project = Project('.')
    # ... perform refactorings ...
finally:
    project.close()

6. Use Context Managers

Create a context manager for automatic cleanup:

from contextlib import contextmanager

@contextmanager
def rope_project(path):
    project = Project(path)
    try:
        yield project
    finally:
        project.close()

# Usage
with rope_project('.') as project:
    # ... perform refactorings ...

Common Workflows

Workflow: Safe Rename Across Project

from rope.base.project import Project
from rope.base import libutils
from rope.refactor.rename import Rename

with rope_project('.') as project:
    # Validate first
    project.validate(project.root)

    # Find the target
    resource = libutils.path_to_resource(project, 'mymodule.py')

    # Read file to find offset
    source = resource.read()
    offset = source.find('old_name')

    # Create renamer
    renamer = Rename(project, resource, offset)

    # Preview
    changes = renamer.get_changes('new_name', docs=True)
    print(changes.get_description())

    # Confirm and apply
    response = input("Apply changes? (y/n): ")
    if response.lower() == 'y':
        project.do(changes)
        print("Refactoring complete!")

Workflow: Extract Method for Code Cleanup

from rope.refactor.extract import ExtractMethod

with rope_project('.') as project:
    resource = libutils.path_to_resource(project, 'messy_module.py')

    # Calculate offsets for the code block to extract
    source = resource.read()
    # Find start/end positions...
    start = source.find('# START EXTRACTION')
    end = source.find('# END EXTRACTION')

    extractor = ExtractMethod(project, resource, start, end)
    changes = extractor.get_changes('extracted_logic', similar=True)

    project.do(changes)

Workflow: Batch Restructure

from rope.refactor.restructure import Restructure

# Convert all old-style format strings to f-strings
pattern = '"${text}" % ${args}'
goal = 'f"${text}"'  # Note: simplified, real implementation is more complex

with rope_project('.') as project:
    restructuring = Restructure(project, pattern, goal, {})
    changes = restructuring.get_changes()

    if changes:
        print(changes.get_description())
        project.do(changes)

Using Helper Scripts

This skill includes helper scripts for common rope operations:

scripts/rope_rename.py

Interactive rename script:

python scripts/rope_rename.py /path/to/project file.py old_name new_name

scripts/rope_extract.py

Extract method/variable interactively:

python scripts/rope_extract.py /path/to/project file.py start_line end_line extracted_name

See the scripts directory for more utilities.

Troubleshooting

Import Errors

If rope can't find imports:

• Ensure the project root is correct
• Check .ropeproject/config.py for python_path settings
• Validate project before refactoring

Incorrect Refactorings

If rope makes wrong changes:

• Run SOA to improve type inference
• Check that offsets are calculated correctly (DOS line endings!)
• Use preview to inspect changes before applying
• Consider limiting scope with resources parameter

Performance Issues

For large projects:

• Use resources parameter to limit refactoring scope
• Run SOA periodically, not on every refactoring
• Consider using .ropeproject caching
• Use TaskHandle to monitor and cancel long operations

References

For detailed information, refer to:

• Rope documentation: https://rope.readthedocs.io/
• Library usage: https://rope.readthedocs.io/en/latest/library.html
• Rope repository: https://github.com/python-rope/rope

See references/rope_library_docs.md for the complete rope library documentation (included in this skill for offline reference).