vmx 2.6.1

Hierarchical, lifecycle-aware MVVM viewmodel framework.

vmx — Python

Hierarchical lifecycle-aware MVVM viewmodel framework for Python, spec-compatible with the C#, TypeScript, and Swift (subset) flavors.

1. Status

v2.6.0 — implements spec-v2.6.0 end-to-end. 232/232 library conformance IDs pass. Supports Python 3.10–3.13. mypy --strict clean. Opt-in vmx.notifications subpackage ships an INotificationHub for async confirmations. A Swift flavor sibling lands as a skeleton at langs/swift/ (subset of spec-v2.6.0); see ../swift/README.md §5 for the in / deferred matrix.

2. Install

pip install vmx
# or
uv add vmx

3. Quick start

The minimum-viable shape is imports → services → builder (name + model + services + optional modeled_hinter) → construct() → read status:

from dataclasses import dataclass

from vmx import (
    ComponentVMOf,
    CompositeVM,
    MessageHub,
    RxDispatcher,
)


@dataclass
class TabModel:
    title: str


# 1. Services (a hub + a dispatcher).
hub = MessageHub()
dispatcher = RxDispatcher.immediate()

# 2. Build leaves: name, model, services, optional modeled_hinter.
home: ComponentVMOf[TabModel] = (
    ComponentVMOf.builder()
    .name("home")
    .model(TabModel("Home"))
    .modeled_hinter(lambda m: m.title)  # optional — defaults to lambda _m: ""
    .services(hub, dispatcher)
    .build()
)

settings: ComponentVMOf[TabModel] = (
    ComponentVMOf.builder()
    .name("settings")
    .model(TabModel("Settings"))
    .services(hub, dispatcher)
    .build()
)

# 3. Build a composite over the leaves.
tabs = (
    CompositeVM[ComponentVMOf[TabModel]]
    .builder()
    .name("tab-bar")
    .services(hub, dispatcher)
    .children(lambda: [home, settings])
    .build()
)

# 4. Transition the lifecycle from CREATED → CONSTRUCTED before use.
tabs.construct()
print(tabs.status)  # ConstructionStatus.CONSTRUCTED

tabs.current = settings
print(tabs.current.model.title)  # "Settings"

tabs.dispose()
hub.dispose()

Tips:

• .modeled_hinter(...) is optional on every modeled builder; the default is lambda _m: "". Pass a callable when you want to derive a display hint from the model.
• For tests, samples, and headless code, NULL_MESSAGE_HUB and NULL_DISPATCHER are safe no-op singletons. Annotate variables as MessageHubProto[Message] (the structural Protocol) to keep mypy --strict happy, or use the generic null_message_hub_of(MyMessage) factory for a narrower message type.

The C# and TypeScript flavors mirror this shape: see C# Quick start and TypeScript Quick start — only the identifier casing differs.

See docs/getting-started/python.md for the full walkthrough.

3.1 Cross-language naming

The conceptual surface is identical across the four flavors; identifier casing follows the per-language idiom (see ADR-0006).

Concept	C#	Python	TypeScript	Swift
Unmodeled VM	ComponentVM	ComponentVM	ComponentVM	ComponentVM
Modeled VM	ComponentVM<M>	ComponentVMOf[M]	ComponentVMOf<M>	ComponentVMOf<M>
Status property	Status	status	status	status
Builder entrypoint	Builder()	builder()	builder()	builder()
Null hub singleton	NullMessageHub.Instance	NULL_MESSAGE_HUB	NullMessageHub.INSTANCE	NullMessageHub.INSTANCE

C# uses PascalCase, Python uses snake_case, TypeScript and Swift use camelCase. The single substantive divergence is that C# names the modeled variant with a generic-parameter suffix (ComponentVM<M>), while Python, TypeScript, and Swift use a separate ComponentVMOf type because their generics syntax cannot overload an unparameterised name.

4. API surface

The public API is re-exported from a single entry point:

from vmx import ...  # see vmx/__init__.py for the full list

Export	Description
ComponentVM	Leaf viewmodel (no model)
ComponentVMOf[M]	Leaf viewmodel with a typed model
ReadonlyComponentVMOf[M]	Leaf VM with read-only model
CompositeVM[VM] / CompositeVMOf[M,VM]	Ordered collection + current slot
GroupVM[VM]	Collection without current selection
AggregateVM1..6[…]	Fixed-arity named component slots (arity 6 added in spec v2.2.0 — see ADR-0034)
ForwardingComponentVM	Decorator for ComponentVMOfProto
ForwardingCompositeVM	Decorator for composites
RelayCommand / RelayCommandOf[T]	Executable command with can_execute predicate
CompositeCommand	Aggregate N inner commands (spec v2.0)
DecoratorCommand	Wrap a command with pre/post + can-execute gate
ConfirmationDecoratorCommand	Wrap a command with an async confirm coroutine
ModeledCrudCommands[M,VM]	Create / UpdateCurrent / DeleteCurrent helper
MessageHub	Pub/sub hub backed by reactivex Subject
NullMessageHub / NULL_MESSAGE_HUB	Null-object variant per ADR-0017
RxDispatcher	Foreground/background scheduler pair
NullDispatcher / NULL_DISPATCHER	Null-object variant per ADR-0017
ConstructionStatus	5-state lifecycle enum
StatusTransitionError	Raised on illegal lifecycle operations
BuilderValidationError	Raised when a builder is missing required fields
walk(root)	DFS pre-order tree traversal generator
walk_expanded(root)	DFS walk gated on IExpandable.is_expanded (v2.0)
find(root, predicate)	Short-circuit tree search
DerivedProperty[TValue] / from_sources(...)	N-source computed value (spec v2.0)
ExpandableState	IExpandable+ICollapsible helper (spec v2.0)
SearchableState[T]	Debounced filter helper (spec v2.0)
ILocalizer / NullLocalizer / NULL_LOCALIZER	i18n hook + null-default (v2.0)
22× capability ABCs	vmx.capabilities.* — opt-in (spec v2.0+)
HierarchicalVM[TModel, TVM]	Recursive tree-structured VM (spec v2.1)
TreeStructureChangedMessage	Tree-structural-change notification (spec v2.1)
FormVM[TM]	Snapshot/revert form lifecycle (spec v2.1)
DialogService / NullDialogService	File/confirm/notify dialogs + null (spec v2.1)
ServicedObservableCollection[T]	Hub-aware observable collection (spec v2.1)
ObservableList[T]	Granular per-mutation events (spec v2.1)
ObservableDictionary[K1, K2, V]	Multi-key observable dictionary (spec v2.1)
PagedComposition[TVM]	Pageable iterable decorator (spec v2.1)
Fluent command helpers	confirm / precede_with / succeed_with / wrap_with over commands (spec v2.1)
property_value_changed_messages_for	Hub helper yielding an observable of property-value snapshots (spec v2.1)

The opt-in vmx.notifications subpackage (spec v2.0+) adds:

Export	Description
Notification / NotificationType / NotificationReaction	Notification primitives
INotificationHub / NotificationHub / NullNotificationHub / NULL_NOTIFICATION_HUB	Async notification hub + null variant
make_confirm(hub, prompt)	Bridge to ConfirmationDecoratorCommand
NotificationVM	Render-side VM for Notification (spec v2.1)
ConfirmationVM	Render-side VM with Approve/Reject (spec v2.1)

5. Conformance

All 232 library conformance IDs from spec/12-conformance.md are covered (the 5 THEME scenario IDs live in the flagship example apps — see CONTRIBUTING §2.5). Test-layout conventions for the conformance tree are documented in tests/conformance/README.md.

v1.x   LIFE-001..013  HUB-001..007  PROP-001..004  CMD-001..007
       CVM-001..006   COMP-001..013 GRP-001..006   AGG-001..005
       FWD-001..003   BLD-001..004  THR-001..004   UTIL-001..003
v2.0   CAP-001..020   NULL-001..003 DPROP-001..012 CMDD-001..009
       NOTIF-001..010 COMP-014..024 GRP-007..010   EXP-001..005
       LOC-001..003
v2.1   HIER-001..014  DIA-001..008  FORM-001..010  NOTIF-011..016
       COL-001..023   CMD-008..011  CAP-021..022
v2.2   AGG-006
v2.3   BLD-005        FORM-011..013 HIER-015..017
v2.4   THEME-001..005
v2.5   HIER-018       NOTIF-017     FORM-014
v2.6   COMP-025..026

Run the suite:

uv run pytest

6. Development

# From this directory
uv sync --all-extras
uv run pytest
uv run ruff check
uv run ruff format --check
uv run mypy --strict src/vmx

The lifecycle-transitions.json fixture from spec/fixtures/ is shipped inside the wheel via hatchling's force-include mapping in pyproject.toml and consumed at runtime by vmx.lifecycle.transition_validator.

7. Releasing

See RELEASING.md for the PyPI release pipeline runbook.

8. License

MIT — see LICENSE.