Python Code Refactoring Analyser

When the user wants to refactor code, improve code quality, or check for code smells:

1. Introduction

This skill provides comprehensive refactoring guidance for Python code, focusing on:

• Functional programming patterns - Detect non-functional code (mutations, side effects, classes vs functions)
• Code quality checks - Automated analysis using pylint, black, and mypy
• Manual refactoring guidance - Identify code smells and suggest improvements
• Configuration extraction - Find hardcoded values that should be extracted to constants or config files

The skill combines automated tool-based analysis with manual pattern detection to provide actionable refactoring suggestions.

2. When to Use

Activate this skill when the user:

• Requests code review or refactoring
• Wants to improve code quality before committing
• Needs to convert object-oriented code to functional style
• Asks to check for code smells or antipatterns
• Wants periodic code quality checks
• Is preparing code for testing (making it more testable)

3. Quick Start

Execute the Python script located in the same directory as this skill:

Auto-detect mode (analyses all Python files in current directory):

python3 skills/refactor/refactor.py

Specific file mode:

python3 skills/refactor/refactor.py path/to/file.py

Full project scan (analyses all .py files recursively):

python3 skills/refactor/refactor.py --all

The script works immediately with no dependencies (uses Python stdlib). Optional tools (pylint, black, mypy) provide enhanced analysis if installed.

4. What It Checks

Functional Programming Patterns (AST-based)

• Mutations: Detects list.append(), dict[key] = value, items[0] = x
• Class usage: Flags classes when functions + dataclasses would suffice
• Global state: Identifies global variable modifications
• Side effects: Finds print(), file I/O, network calls in business logic functions
• Impure functions: Detects functions that modify state or have side effects

Code Quality (via pylint)

• PEP 8 style compliance
• Naming conventions
• Code complexity metrics
• Unused imports and variables
• Missing docstrings
• Potential bugs

Code Formatting (via black)

• Line length consistency
• Indentation style
• Quote style
• Whitespace formatting

Type Safety (via mypy)

• Type hint coverage
• Type correctness
• Return type consistency
• Argument type validation

Manual Code Smell Detection

• Functions longer than 50 lines
• Nesting depth greater than 3 levels
• Magic numbers and strings (hardcoded values)
• Missing or inadequate docstrings
• Repeated code patterns (DRY violations)

Configuration Extraction

• Hardcoded file paths, URLs, API keys
• Environment-specific values
• Magic constants that should be named
• Format strings and patterns

5. Output Interpretation

The script produces a structured report with issues grouped by severity and category:

Severity Levels

• CRITICAL: Must fix - violates core principles or will cause bugs
• WARNING: Should fix - reduces code quality or maintainability
• INFO: Consider fixing - minor improvements or suggestions

Example Output

Refactoring Analysis: skills/anonymise/anonymise.py
================================================================

SUMMARY: 5 issues found
  Critical: 0
  Warning: 3
  Info: 2

FUNCTIONAL PATTERNS (2 warnings)
  Line 52: Side effect detected in function 'anonymise_csv'
    Suggestion: Extract file I/O to separate function, keep core logic pure

  Line 70: Mutation detected - modifying list in place
    Suggestion: Use list comprehension or functional transformation

CODE QUALITY (1 warning)
  [pylint] Line 54: Consider using 'with' statement for resource cleanup
    Score: 9.2/10

INFO (2)
  [config] Line 50: Hardcoded datetime format string
    Suggestion: Extract to constant TIMESTAMP_FORMAT = "%Y%m%d_%H%M%S"

  [code smell] Function 'main' is 45 lines - approaching complexity threshold
    Suggestion: Consider extracting argument parsing to separate function

Checks run: AST analysis, pylint, black, mypy
Tools available: pylint ✓, black ✓, mypy ✓

6. Tool Integration

First-Run Setup

The script automatically checks for optional analysis tools. If tools are not installed:

Optional tools not found:
  - pylint: pip install pylint
  - black: pip install black
  - mypy: pip install mypy

Install all: pip install pylint black mypy

Continuing with stdlib-only analysis...

Note: Core functional pattern analysis and code smell detection work without any external dependencies.

Configuration Files

On first run, the script can generate configuration files if they don't exist:

pyproject.toml - Configures black, mypy, and pylint:

• Line length: 88 characters (black default)
• Python version: 3.8+
• Type checking: Strict mode
• Functional-programming-friendly linter rules

You can customise these configs for project-specific requirements.

Tool Execution

• Graceful degradation: Skips unavailable tools without errors
• Unified output: Parses all tool outputs into consistent Issue format
• Performance: Caches results during analysis for speed

7. Manual Refactoring Guidance

Extracting Configuration

Before (hardcoded values):

timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
output_file = f"{timestamp}.csv"

After (extracted constants):

TIMESTAMP_FORMAT = "%Y%m%d_%H%M%S"
CSV_EXTENSION = ".csv"

timestamp = datetime.now().strftime(TIMESTAMP_FORMAT)
output_file = f"{timestamp}{CSV_EXTENSION}"

Converting to Functional Style

Before (mutation-based):

def process_items(items):
    results = []
    for item in items:
        if item > 0:
            results.append(item * 2)
    return results

After (functional):

def process_items(items: list[int]) -> list[int]:
    return [item * 2 for item in items if item > 0]

Extracting Pure Functions

Before (side effects mixed with logic):

def anonymise_csv(input_file: str) -> str:
    with open(input_file, 'r') as f:
        rows = list(csv.reader(f))

    anonymised = [row[1:] for row in rows]

    with open(output_file, 'w') as f:
        csv.writer(f).writerows(anonymised)

    return output_file

After (pure core, impure shell):

def read_csv(file_path: str) -> list[list[str]]:
    """Read CSV file (impure I/O)."""
    with open(file_path, 'r') as f:
        return list(csv.reader(f))

def anonymise_rows(rows: list[list[str]]) -> list[list[str]]:
    """Remove first column from all rows (pure function)."""
    return [row[1:] for row in rows]

def write_csv(file_path: str, rows: list[list[str]]) -> None:
    """Write CSV file (impure I/O)."""
    with open(file_path, 'w') as f:
        csv.writer(f).writerows(rows)

def anonymise_csv(input_file: str, output_file: str) -> str:
    """Orchestrate anonymisation (impure shell)."""
    rows = read_csv(input_file)
    anonymised = anonymise_rows(rows)
    write_csv(output_file, anonymised)
    return output_file

Function Decomposition

When to break down functions:

• Function exceeds 50 lines
• Cyclomatic complexity > 10
• Multiple levels of nesting (> 3)
• Mixing different levels of abstraction
• Repeated code blocks

How to decompose:

1. Identify distinct responsibilities
2. Extract each responsibility to a named function
3. Use descriptive function names
4. Pass dependencies explicitly (no hidden state)
5. Prefer pure functions where possible

8. Notes

• British English: All output uses British spelling (analyse, optimise, behaviour, etc.)
• Non-destructive: Analysis only - no automatic code modifications
• Platform-agnostic: Works with any AI coding assistant (Claude Code, Cursor, Aider, Codex CLI, etc.)
• Minimal dependencies: Core analysis uses stdlib only; external tools are optional enhancements
• Testability focus: Suggestions prioritise making code easier to test with pytest
• Functional-first: Recommendations align with project preference for functional programming idioms
• Standards compliance: Checks against AGENTS.md conventions (PEP 8, type hints, British English, functional style)