Python Development

--- name: python-development description: "Python and wxPython development reference patterns, common pitfalls, framework-specific guides, desktop accessibility APIs, and cross-platform considerations. Use when building, debugging, packaging, or reviewing Python desktop applications."

Python Development Skill

Reference data for the Developer Hub, Python Specialist, and wxPython Specialist agents.

Python Version Quick Reference

pyproject.toml Skeleton

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

[project]
name = "my-app"
version = "1.0.0"
requires-python = ">=3.10"
dependencies = []

[project.optional-dependencies]
dev = ["pytest>=8.0", "ruff>=0.6", "mypy>=1.11"]

[project.scripts]
myapp = "my_app.__main__:main"

[tool.pytest.ini_options]
testpaths = ["tests"]
addopts = "-ra --strict-markers"

[tool.ruff]
target-version = "py310"
line-length = 100

[tool.ruff.lint]
select = ["E", "F", "W", "I", "N", "UP", "B", "SIM", "TCH"]

[tool.mypy]
python_version = "3.10"
strict = true

PyInstaller Quick Reference

One-File Mode

exe = EXE(pyz, a.scripts, a.binaries, a.zipfiles, a.datas,
          name='MyApp', console=False, icon='icon.ico')

One-Folder Mode

exe = EXE(pyz, a.scripts, exclude_binaries=True,
          name='MyApp', console=False, icon='icon.ico')
coll = COLLECT(exe, a.binaries, a.zipfiles, a.datas, name='MyApp')

Common Hidden Imports

• pkg_resources.extern
• accessible_output2 (for a11y desktop apps)
• keyring.backends (for credential storage)
• platformdirs
• httpx._transports / httpcore._backends
• encodings (always needed)

wxPython Quick Reference

Sizer Cheat Sheet

Thread-Safe GUI Updates

# From worker thread:
wx.CallAfter(self.update_status, "Done")
wx.PostEvent(self, CustomEvent(data=result))

# NEVER do this from a worker thread:
self.status_bar.SetStatusText("Done")  # CRASH or CORRUPTION

Standard IDs

Event Types

Common Pitfalls

Python

• Mutable default arguments: def f(items=[]) shares the list across calls. Use None and create inside.
• Late binding closures: lambda: x in a loop captures the variable, not the value. Use lambda x=x: x.
• Circular imports: Move imports inside functions, use TYPE_CHECKING block, or restructure modules.
• field() outside dataclass: field() is only valid inside @dataclass classes. Use plain type annotations elsewhere.
• is vs ==: is checks identity, == checks equality. Use is only for None, True, False.
• String concatenation in loops: Use "".join() or io.StringIO instead.

wxPython

• GUI from worker thread: Always use wx.CallAfter() or wx.PostEvent().
• Missing event.Skip(): Other handlers won't fire. Call event.Skip() unless you intentionally consume the event.
• Timer not stopped: Stop timers in EVT_CLOSE handler to prevent callbacks after destruction.
• AUI not uninitialized: Call _mgr.UnInit() in close handler.
• Dialog not destroyed: Use context managers (with MyDialog(...) as dlg:) for automatic cleanup.
• Wrong parent for sizer items: All controls in a sizer must have the same parent panel.
• Absolute positioning: Never use SetPosition() or SetSize() for layout. Always use sizers.

Cross-Platform Paths

from platformdirs import user_config_dir, user_data_dir, user_cache_dir

config = user_config_dir("MyApp", "MyCompany")  # %APPDATA% / ~/Library/... / ~/.config/
data = user_data_dir("MyApp", "MyCompany")
cache = user_cache_dir("MyApp", "MyCompany")

Testing Quick Reference

# Run all tests
pytest

# Run specific test file
pytest tests/test_queue.py

# Run specific test
pytest tests/test_queue.py::test_submit_job -v

# With coverage
pytest --cov=mypackage --cov-report=term-missing

# Stop on first failure
pytest -x

# Show locals on failure
pytest -l

Logging Setup Template

import logging

def setup_logging(level: int = logging.INFO) -> None:
    logging.basicConfig(
        level=level,
        format="%(asctime)s %(name)s %(levelname)s %(message)s",
        datefmt="%Y-%m-%d %H:%M:%S",
    )
    # Quiet noisy libraries
    logging.getLogger("httpx").setLevel(logging.WARNING)
    logging.getLogger("httpcore").setLevel(logging.WARNING)

Desktop Accessibility Quick Reference

Platform API Summary

wxPython Accessibility

# Set accessible name (screen reader label)
control.SetLabel("Descriptive Label")

# Set accessible description (supplementary info)
# Use wx.AccessibleDescription or wx.Accessible subclass

# Keyboard navigation
control.SetFocus()           # Move focus programmatically
panel.SetFocusIgnoringChildren()  # Focus the panel itself