e501-fixer 0.1.0

Automatic string literal wrapping for PEP 8 E501 compliance

e501-fixer

Automatic string literal wrapping for PEP 8 E501 compliance.

Problem

PEP 8 recommends a maximum line length of 88 characters. When strings exceed this limit, Python developers must manually wrap them—a tedious, error-prone process. While tools like Black and ruff exist, none provide comprehensive automatic wrapping of string literals.

e501-fixer fills this gap with a safe, well-tested solution that automatically wraps long strings using Python's implicit string concatenation.

Features

• ✅ Automatic string wrapping using implicit concatenation
• ✅ Preserves quote style (single vs. double quotes)
• ✅ Handles all string types (regular, raw, byte strings)
• ✅ Safe by default (skips f-strings and triple-quoted strings)
• ✅ CLI interface for easy integration into workflows
• ✅ Pre-commit hook support for automated checks
• ✅ 100% test coverage with comprehensive test suite
• ✅ Type-safe with full mypy strict mode compliance

Installation

Via pip (when published to PyPI)

pip install e501-fixer

From source (development)

Clone the standalone e501-fixer repository:

git clone https://github.com/muunkky/e501-fixer.git
cd e501-fixer
pip install -e .

With CLI support

pip install -e ".[cli]"

Quick Start

CLI Usage

# Fix E501 violations in a file
e501-fixer fix myfile.py

# Fix violations in a directory
e501-fixer fix src/

# Check for violations without fixing
e501-fixer check myfile.py

# Check with custom line length
e501-fixer fix --max-line-length 100 myfile.py

Python API

from e501_fixer import FileProcessor
from pathlib import Path

# Create processor with custom line length
processor = FileProcessor(max_line_length=100)

# Process single file
result = processor.process_file(Path("example.py"))
print(f"Fixed {result.fixes_applied} violations")

# Process directory
result = processor.process_directory(Path("src/"))
print(f"Fixed {result.total_fixes} violations in {result.files_processed} files")

How It Works

Before

def greet(name: str) -> None:
    message = "Hello, this is a very long string that exceeds the PEP 8 line length limit and needs to be wrapped"
    print(message)

After

def greet(name: str) -> None:
    message = (
        "Hello, this is a very long string that exceeds the "
        "PEP 8 line length limit and needs to be wrapped"
    )
    print(message)

Examples

Preserving Quote Style

# Input: single quotes
description = 'This is a long single-quoted string that needs wrapping and is quite verbose'

# Output: single quotes preserved
description = (
    'This is a long single-quoted string that needs wrapping '
    'and is quite verbose'
)

Respecting Indentation

# Input: nested string
def setup():
    if True:
        config = "This is a very long configuration string that exceeds the maximum line length and must be wrapped properly"

# Output: indentation respected
def setup():
    if True:
        config = (
            "This is a very long configuration string that exceeds "
            "the maximum line length and must be wrapped properly"
        )

Raw Strings

# Input: raw string
pattern = r'This is a very long regex pattern that exceeds the line length and needs to be wrapped for readability'

# Output: raw string type preserved
pattern = (
    r'This is a very long regex pattern that exceeds the line '
    r'length and needs to be wrapped for readability'
)

Pre-commit Integration

Add to .pre-commit-config.yaml:

- repo: local
  hooks:
    - id: e501-fixer
      name: e501-fixer
      entry: e501-fixer fix
      language: system
      types: [python]
      stages: [commit]

Or using the pre-commit hooks defined in this package (when published):

- repo: https://github.com/muunkky/e501-fixer
  rev: v0.1.0
  hooks:
    - id: e501-fix      # Auto-fix violations
    - id: e501-check    # Check without modifying (for CI)

The package provides two hooks:

• e501-fix: Automatically fixes E501 violations (use before commit)
• e501-check: Reports violations without modifying (use in CI/CD)

Safety Guarantees

• No Code Corruption: Conservative approach—skips uncertain cases
• Preserves Semantics: Implicit concatenation produces identical behavior
• Type Safe: Full mypy strict mode compliance
• Well Tested: 90+ tests covering all string types and edge cases
• Documented: Comprehensive architecture documentation (ADR-018)

Architecture

The tool is built on a modular, TDD-driven architecture:

• StringLiteralParser: Identifies and extracts string literals using regex
• BreakPointFinder: Calculates optimal positions to split strings
• StringWrapper: Applies wrapping transformations
• FileProcessor: Orchestrates parsing, wrapping, and file I/O

For detailed architecture, see ARCHITECTURE.md.

Performance

• Per-file: ~1-2ms for average files (100-200 lines)
• Large files: <100ms for 1000+ line files
• Directory processing: Efficient batch handling

Configuration

Line Length

e501-fixer fix --max-line-length 100 myfile.py

Python API:

processor = FileProcessor(max_line_length=100)

Indentation

processor = FileProcessor(default_indentation="  ")  # 2 spaces

Limitations

• F-strings: Not wrapped (interpolations make splitting risky)
• Triple-quoted strings: Not wrapped (complex semantics)
• Unbreakable strings: Strings without spaces cannot be wrapped

These are conservative choices that prioritize safety over coverage.

Troubleshooting

No violations found

• Verify the file has strings exceeding the max line length
• Check --max-line-length setting (default: 88)
• Some strings may be intentionally unbreakable (no spaces)

Pre-commit hook not executing

• Ensure e501-fixer is installed in the pre-commit environment
• Check .pre-commit-config.yaml syntax
• Run pre-commit install to activate hooks

Import errors

• Install CLI dependencies: pip install e501-fixer[cli]
• Verify Python 3.10+ is installed

Development

Setup

pip install -e ".[dev]"

Testing

pytest tests/
pytest --cov=e501_fixer

Type Checking

mypy e501_fixer/

Linting

ruff check e501_fixer/

License

MIT - see LICENSE file

Contributing

Contributions are welcome! Please ensure:

• All tests pass (pytest)
• Code passes type checking (mypy)
• Code passes linting (ruff check)
• New features include tests and documentation

References

• PEP 8 - Style Guide for Python Code
• E501 - Line too long
• ADR-018 - E501 String Literal Fixer Architecture
• Black Code Formatter