python-development

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

[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

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

# 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

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

Platform	API	Python Binding	Use For
Windows	UI Automation (UIA)	comtypes, pywinauto	Modern apps, NVDA/Narrator
Windows	MSAA / IAccessible2	comtypes, pywinauto	Legacy apps, JAWS
macOS	NSAccessibility	pyobjc	VoiceOver

wxPython Accessibility Essentials

# Name every control that lacks a visible label
# CORRECT: use StaticText immediately before the control in the sizer
label = wx.StaticText(panel, label="Scan progress:")
# ctrl = wx.Gauge(panel)  -- add label to sizer right before ctrl
# WRONG: SetName() is ignored by screen readers
# ctrl.SetName("Scan progress")  -- only affects FindWindowByName()

# Tab order follows sizer insertion order; override with:
ctrl2.MoveAfterInTabOrder(ctrl1)

# Keyboard shortcuts via accelerator table
accel = wx.AcceleratorTable([
    (wx.ACCEL_CTRL, ord('S'), wx.ID_SAVE),
    (wx.ACCEL_CTRL, ord('Q'), wx.ID_EXIT),
])
frame.SetAcceleratorTable(accel)

# Platform-correct button order in dialogs
sizer.Add(dialog.CreateStdDialogButtonSizer(wx.OK | wx.CANCEL))

Screen Reader Interaction Model

Screen readers expose controls as: Name + Role + Value + State

Property	wxPython Source	Example
Name	Preceding wx.StaticText, label= parameter, or SetToolTip()	"Scan progress"
Role	Widget type (automatic)	button, text field, list
Value	Widget content	"75%", "Hello world"
State	Widget flags	focused, disabled, checked

Desktop A11y Checklist

1. Every control has a meaningful name (preceding wx.StaticText for inputs, label= for buttons, SetToolTip() for image-only controls)
2. Keyboard-only operation -- every action reachable via Tab/Enter/Space/arrows
3. Focus visible -- never suppress focus indicators
4. Tab order is logical (generally top-to-bottom, left-to-right)
5. Color is not the sole information carrier
6. High contrast mode supported (use system colors, not hardcoded)
7. Dialogs use CreateStdDialogButtonSizer() for platform-correct button order
8. AUI panes are keyboard-navigable

Structured Audit Rule Sets

When audit mode is activated, agents use these structured detection rule sets:

Rule Prefix	Agent	Scope	Count
WX-A11Y-001..012	wxpython-specialist	wxPython-specific patterns (StaticText labels, AcceleratorTable, mouse-only events, dialogs)	12 rules
DTK-A11Y-001..012	desktop-a11y-specialist	Platform-level API patterns (Name/Role/State/Value, focus, UIA/NSAccessibility)	12 rules
TST-A11Y-001..010	desktop-a11y-testing-coach	Test coverage gaps (automated tests, SR testing, keyboard plans, CI integration)	10 rules

Rule sets don't overlap -- WX covers wxPython widget patterns, DTK covers platform APIs, TST covers testing process gaps.

Agent Routing

For deeper expertise, the skill routes to these specialists:

• desktop-a11y-specialist -- Platform API implementation, wx.Accessible, custom widget patterns (DTK-A11Y-* audit rules)
• desktop-a11y-testing-coach -- NVDA/JAWS/Narrator testing, Accessibility Insights, automated UIA tests (TST-A11Y-* audit rules)
• a11y-tool-builder -- Rule engine architecture, document parsers, severity scoring, report generators