Agent skill

python-development

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.

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Install this agent skill to your Project

npx add-skill https://github.com/Community-Access/accessibility-agents/tree/main/.gemini/extensions/a11y-agents/skills/python-development

SKILL.md

Python Development Skill

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

Python Version Quick Reference

Version Key Features EOL
3.10 match/case, X | Y unions, ParamSpec Oct 2026
3.11 Exception groups, Self type, tomllib, faster CPython Oct 2027
3.12 Type parameter syntax def f[T](), @override, f-string nesting Oct 2028
3.13 Experimental free-threaded mode, improved error messages Oct 2029
3.14 async pdb.set_trace_async(), template strings (PEP 750) Oct 2030

pyproject.toml Skeleton

toml
[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

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

One-Folder Mode

python
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

Sizer When to Use
wx.BoxSizer(wx.VERTICAL) Stack items top-to-bottom
wx.BoxSizer(wx.HORIZONTAL) Lay items left-to-right
wx.GridBagSizer(vgap, hgap) Form layouts with labels + controls
wx.FlexGridSizer(rows, cols, vgap, hgap) Even grid layouts
wx.WrapSizer Flow layout that wraps
wx.StaticBoxSizer(wx.VERTICAL, parent, "Label") Grouped controls with border

Thread-Safe GUI Updates

python
# 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

ID Purpose
wx.ID_OK OK button
wx.ID_CANCEL Cancel button
wx.ID_SAVE Save action
wx.ID_OPEN Open action
wx.ID_EXIT Exit / Quit
wx.ID_HELP Help action
wx.ID_NEW New document
wx.ID_UNDO / wx.ID_REDO Undo / Redo

Event Types

Event Trigger
wx.EVT_BUTTON Button click
wx.EVT_MENU Menu item selected
wx.EVT_CLOSE Window close requested
wx.EVT_SIZE Window resized
wx.EVT_TIMER Timer fired
wx.EVT_TEXT Text control content changed
wx.EVT_LIST_ITEM_SELECTED List item selected
wx.EVT_TREE_SEL_CHANGED Tree selection changed
wx.EVT_UPDATE_UI UI state update check

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

python
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

bash
# 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

python
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

Platform API Python Binding
Windows UI Automation comtypes + UIAutomationCore
Windows MSAA/IAccessible2 pyia2, comtypes
macOS NSAccessibility pyobjc-framework-Cocoa

wxPython Accessibility

python
# 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

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