Python Quality Checker Skill

Purpose

This skill provides comprehensive Python code quality validation including formatting (Black), type checking (mypy), linting (flake8/ruff), security analysis (bandit), and complexity analysis. Ensures code meets Python best practices and project standards.

When to Use

• Validating Python code quality before commit
• Running pre-commit quality checks
• CI/CD quality gate validation
• Code review preparation
• Ensuring PEP 8 compliance
• Type safety validation
• Security vulnerability detection

Quality Check Workflow

1. Environment Setup

Verify Tools Installed:

# Check Python version
python --version

# Check quality tools
black --version
mypy --version
flake8 --version
bandit --version

# Or install missing tools
pip install black mypy flake8 bandit ruff

Install Development Dependencies:

# Install all dev tools
pip install -e ".[dev]"

# Or from requirements
pip install -r requirements-dev.txt

Deliverable: Quality tools ready

---

2. Code Formatting Check (Black)

Check Formatting:

# Check if code is formatted
black --check src/ tests/

# Check with diff
black --check --diff src/ tests/

# Check specific files
black --check src/tools/feature/core.py

# Check with color output
black --check --color src/ tests/

Auto-Format Code:

# Format all code
black src/ tests/

# Format specific directory
black src/tools/feature/

# Format with specific line length
black --line-length 100 src/

# Preview changes without applying
black --check --diff src/

Configuration (pyproject.toml):

[tool.black]
line-length = 88
target-version = ['py311']
include = '\.pyi?$'
extend-exclude = '''
/(
  # Directories
  \.eggs
  | \.git
  | \.venv
  | build
  | dist
)/
'''

Deliverable: Formatting validation report

---

3. Type Checking (mypy)

Run Type Checks:

# Check entire codebase
mypy src/

# Check specific module
mypy src/tools/feature/

# Check with stricter settings
mypy --strict src/

# Show error codes
mypy --show-error-codes src/

# Generate HTML report
mypy --html-report mypy-report/ src/

Common Type Issues:

# Check for missing type hints
mypy --disallow-untyped-defs src/

# Check for Any types
mypy --disallow-any-explicit src/

# Check for incomplete definitions
mypy --check-untyped-defs src/

Configuration (pyproject.toml):

[tool.mypy]
python_version = "3.11"
warn_return_any = true
warn_unused_configs = true
disallow_untyped_defs = true
disallow_incomplete_defs = true
check_untyped_defs = true
no_implicit_optional = true
warn_redundant_casts = true
warn_unused_ignores = true
warn_no_return = true
warn_unreachable = true
strict_equality = true
show_error_codes = true

[[tool.mypy.overrides]]
module = "tests.*"
disallow_untyped_defs = false

Deliverable: Type checking report

---

4. Linting (flake8/ruff)

Flake8 Linting:

# Lint entire codebase
flake8 src/ tests/

# Lint with statistics
flake8 --statistics src/

# Lint with detailed output
flake8 --show-source --show-pep8 src/

# Generate HTML report
flake8 --format=html --htmldir=flake8-report/ src/

Ruff Linting (Faster Alternative):

# Lint with ruff
ruff check src/ tests/

# Auto-fix issues
ruff check --fix src/ tests/

# Show violations
ruff check --output-format=full src/

# Specific rules
ruff check --select=E,F,I src/

Flake8 Configuration (.flake8):

[flake8]
max-line-length = 88
extend-ignore = E203, W503
exclude =
    .git,
    __pycache__,
    .venv,
    venv,
    build,
    dist
max-complexity = 10
per-file-ignores =
    __init__.py:F401

Ruff Configuration (pyproject.toml):

[tool.ruff]
line-length = 88
target-version = "py311"
select = [
    "E",  # pycodestyle errors
    "W",  # pycodestyle warnings
    "F",  # pyflakes
    "I",  # isort
    "N",  # pep8-naming
    "UP", # pyupgrade
    "B",  # flake8-bugbear
    "C4", # flake8-comprehensions
]
ignore = ["E203", "W503"]
exclude = [
    ".git",
    "__pycache__",
    ".venv",
    "build",
    "dist",
]

[tool.ruff.per-file-ignores]
"__init__.py" = ["F401"]

Deliverable: Linting report

---

5. Security Analysis (bandit)

Run Security Checks:

# Basic security scan
bandit -r src/

# Detailed report
bandit -r src/ -f json -o bandit-report.json

# Exclude test files
bandit -r src/ --exclude tests/

# Specific confidence level
bandit -r src/ -ll  # Low confidence
bandit -r src/ -l   # Medium confidence
bandit -r src/      # All levels

# Skip specific issues
bandit -r src/ -s B101,B601

Common Security Issues:

# Check for hardcoded passwords
bandit -r src/ -t B105,B106

# Check for SQL injection
bandit -r src/ -t B608

# Check for command injection
bandit -r src/ -t B602,B603

# Check for unsafe YAML loading
bandit -r src/ -t B506

Configuration (.bandit):

# .bandit
exclude_dirs:
  - /tests/
  - /venv/
  - /.venv/

skips:
  - B101  # Skip assert warnings in production code
  - B601  # Skip shell=True warnings (if justified)

tests:
  - B201  # flask_debug_true
  - B501  # request_with_no_cert_validation
  - B502  # ssl_with_bad_version

Deliverable: Security analysis report

---

6. Import Sorting (isort)

Check Import Organization:

# Check imports
isort --check-only src/ tests/

# Check with diff
isort --check-only --diff src/ tests/

# Auto-fix imports
isort src/ tests/

Configuration (pyproject.toml):

[tool.isort]
profile = "black"
line_length = 88
multi_line_output = 3
include_trailing_comma = true
force_grid_wrap = 0
use_parentheses = true
ensure_newline_before_comments = true

Deliverable: Import sorting validation

---

7. Complexity Analysis

Check Code Complexity:

# Cyclomatic complexity with radon
pip install radon
radon cc src/ -a

# Show complex functions (>10)
radon cc src/ -nc

# Maintainability index
radon mi src/

# Raw metrics
radon raw src/

McCabe Complexity (via flake8):

# Check complexity with flake8
flake8 --max-complexity=10 src/

# Show complexity metrics
pip install flake8-mccabe
flake8 --statistics --select=C src/

Deliverable: Complexity analysis report

---

8. Comprehensive Quality Check

Run All Checks:

#!/bin/bash
# scripts/quality-check.sh

set -e  # Exit on first error

echo "=== Python Quality Checks ==="

echo "1. Code Formatting (Black)..."
black --check src/ tests/

echo "2. Import Sorting (isort)..."
isort --check-only src/ tests/

echo "3. Type Checking (mypy)..."
mypy src/

echo "4. Linting (ruff)..."
ruff check src/ tests/

echo "5. Security Analysis (bandit)..."
bandit -r src/ -ll

echo "6. Complexity Check..."
radon cc src/ -nc

echo "=== All Quality Checks Passed ✅ ==="

Make script executable:

chmod +x scripts/quality-check.sh
./scripts/quality-check.sh

Deliverable: Comprehensive quality report

---

Quality Standards

Code Formatting

• All code formatted with Black
• Line length ≤ 88 characters
• Imports sorted with isort
• Trailing whitespace removed
• Consistent string quotes

Type Checking

• All functions have type hints
• No Any types (except justified)
• No missing return types
• No implicit Optional
• mypy passes with no errors

Linting

• No PEP 8 violations
• No undefined names
• No unused imports
• No unused variables
• Complexity ≤ 10 per function

Security

• No hardcoded secrets/passwords
• No SQL injection vulnerabilities
• No command injection risks
• Safe YAML/pickle usage
• Proper input validation

Code Quality

• Functions < 50 lines
• Files < 500 lines
• Classes < 300 lines
• Max nesting depth: 4
• Cyclomatic complexity < 10

---

Quality Check Matrix

Check	Tool	Threshold	Auto-Fix
Formatting	Black	Must pass	Yes
Type hints	mypy	0 errors	No
Linting	ruff/flake8	0 errors	Partial
Imports	isort	Must pass	Yes
Security	bandit	0 high severity	No
Complexity	radon	≤ 10	No

---

Pre-commit Integration

Setup pre-commit hooks:

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/psf/black
    rev: 23.9.1
    hooks:
      - id: black
        language_version: python3.11

  - repo: https://github.com/pycqa/isort
    rev: 5.12.0
    hooks:
      - id: isort
        args: ["--profile", "black"]

  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: v0.1.0
    hooks:
      - id: ruff
        args: [--fix, --exit-non-zero-on-fix]

  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v1.5.1
    hooks:
      - id: mypy
        additional_dependencies: [types-all]

  - repo: https://github.com/PyCQA/bandit
    rev: 1.7.5
    hooks:
      - id: bandit
        args: ["-ll", "-r", "src/"]

Install and run:

# Install pre-commit
pip install pre-commit

# Install hooks
pre-commit install

# Run manually
pre-commit run --all-files

Deliverable: Pre-commit hooks configured

---

CI/CD Integration

GitHub Actions Example:

# .github/workflows/quality.yml
name: Python Quality Checks

on: [push, pull_request]

jobs:
  quality:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Set up Python
        uses: actions/setup-python@v4
        with:
          python-version: '3.11'

      - name: Install dependencies
        run: |
          pip install black mypy ruff bandit isort radon
          pip install -r requirements.txt

      - name: Check formatting
        run: black --check src/ tests/

      - name: Check imports
        run: isort --check-only src/ tests/

      - name: Type checking
        run: mypy src/

      - name: Linting
        run: ruff check src/ tests/

      - name: Security scan
        run: bandit -r src/ -ll

      - name: Complexity check
        run: radon cc src/ -nc

Deliverable: CI/CD quality pipeline

---

Quality Check Troubleshooting

Black Formatting Failures

# Check what would change
black --check --diff src/

# Apply fixes
black src/

# Check specific file
black --check src/tools/feature/core.py

mypy Type Errors

# Show detailed error
mypy --show-error-codes src/

# Check specific file
mypy src/tools/feature/core.py

# Ignore specific error (last resort)
# type: ignore[error-code]

Ruff/Flake8 Violations

# Show violation details
ruff check --output-format=full src/

# Auto-fix safe violations
ruff check --fix src/

# Ignore specific line (last resort)
# noqa: F401

Bandit Security Issues

# Show detailed report
bandit -r src/ -f json

# Skip false positives
# nosec B101

# Exclude specific tests
bandit -r src/ -s B101,B601

---

Quality Report Template

# Python Quality Check Report

## Summary
- **Status**: ✅ All checks passed
- **Date**: 2024-01-15
- **Code Base**: src/

## Checks Performed

### Formatting (Black)
- **Status**: ✅ PASS
- **Files Checked**: 45
- **Issues**: 0

### Type Checking (mypy)
- **Status**: ✅ PASS
- **Files Checked**: 45
- **Errors**: 0
- **Warnings**: 0

### Linting (ruff)
- **Status**: ✅ PASS
- **Files Checked**: 45
- **Violations**: 0

### Security (bandit)
- **Status**: ✅ PASS
- **Files Scanned**: 45
- **High Severity**: 0
- **Medium Severity**: 0
- **Low Severity**: 2 (acceptable)

### Complexity (radon)
- **Status**: ✅ PASS
- **Average Complexity**: 4.2
- **Max Complexity**: 8
- **Files > 10**: 0

## Details

All Python quality checks passed successfully. Code is well-formatted, type-safe, lint-free, secure, and maintainable.

## Recommendations

- Continue maintaining type hints for all new functions
- Keep cyclomatic complexity below 10
- Run pre-commit hooks before commits

---

Integration with Code Quality Specialist

Input: Python codebase quality check request Process: Run all Python quality tools and analyze results Output: Comprehensive quality report with pass/fail status Next Step: Report to code-quality-specialist for consolidation

---

Best Practices

Development

• Run Black on save (IDE integration)
• Enable mypy in IDE for real-time feedback
• Use pre-commit hooks
• Fix linting issues immediately

Pre-Commit

• Run full quality check script
• Ensure all checks pass
• Fix issues before pushing
• Review security warnings

CI/CD

• Run quality checks on every PR
• Fail build on quality violations
• Generate quality reports
• Track quality metrics over time

Code Review

• Verify quality checks passed
• Review type hints
• Check security scan results
• Validate complexity metrics

---

Supporting Resources

• Black: https://black.readthedocs.io
• mypy: https://mypy.readthedocs.io
• ruff: https://docs.astral.sh/ruff
• bandit: https://bandit.readthedocs.io
• isort: https://pycqa.github.io/isort
• radon: https://radon.readthedocs.io

---

Success Metrics

• All code formatted with Black
• All type checks passing
• Zero linting violations
• No high-severity security issues
• Complexity under threshold
• All quality checks automated