René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Inconsistent typing for WebSocketMessage and WebSocketClient.run() callback in v2.8.0","articleBody":"Hi Massive team,\n\nI noticed an inconsistency in the websocket typing in Massive Python SDK v2.8.0.\n\n`WebSocketMessage` is currently defined as a `NewType` over a list of parsed event models:\n\n```python\nWebSocketMessage = NewType(\n    \"WebSocketMessage\",\n    List[\n        Union[\n            EquityAgg,\n            CurrencyAgg,\n            EquityTrade,\n            ...\n        ]\n    ],\n)\n```\n\nHowever, `WebSocketClient.run()` is typed as accepting a callback of:\n\n```python\nCallable[[List[WebSocketMessage]], None]\n```\n\nThis effectively makes the callback parameter type a nested list-like structure:\n`List[WebSocketMessage]`, while `WebSocketMessage` itself already represents a list\nof parsed websocket events.\n\nThis causes type checkers such as Pyright/Pylance to reject handlers like this:\n\n```python\ndef handle_msg(messages: WebSocketMessage) -\u003e None:\n    for message in messages:\n        if isinstance(message, EquityAgg):\n            ...\n```\n\nwith an error similar to:\n\n```text\nArgument of type \"(messages: WebSocketMessage) -\u003e None\" cannot be assigned to parameter \"handle_msg\"\nType \"(messages: WebSocketMessage) -\u003e None\" is not assignable to type \"(List[WebSocketMessage]) -\u003e None\"\n```\n\nThere also seems to be a related inconsistency in the parser:\n\n```python\ndef parse_single(...) -\u003e Optional[WebSocketMessage]:\n    parsed = model_class.from_dict(data)\n    return cast(WebSocketMessage, parsed)\n```\n\nAt runtime, `parsed` is a single event object such as `EquityAgg`, not a list. Then\n`parse()` returns `List[WebSocketMessage]`.\n\nSo there appear to be two possible fixes:\n\n1. If `WebSocketMessage` is intended to mean a single parsed event, redefine it as\n   a union of event model types, not a list.\n2. If `WebSocketMessage` is intended to mean a batch of parsed events, then `run()`\n   should accept `Callable[[WebSocketMessage], None]`, and `parse_single()` should\n   not cast individual event objects to `WebSocketMessage`.\n\nBased on the current runtime behavior, option 1 seems more natural:\n\n```python\nWebSocketMessage = NewType(\n    \"WebSocketMessage\",\n    Union[\n        EquityAgg,\n        CurrencyAgg,\n        EquityTrade,\n        ...\n    ],\n)\n```\n\nor alternatively, using a type alias instead of `NewType`:\n\n```python\nWebSocketMessage = Union[\n    EquityAgg,\n    CurrencyAgg,\n    EquityTrade,\n    ...\n]\n```\n\nThen these signatures would make sense:\n\n```python\ndef parse_single(...) -\u003e Optional[WebSocketMessage]: ...\ndef parse(...) -\u003e List[WebSocketMessage]: ...\n\ndef run(\n    self,\n    handle_msg: Callable[[List[WebSocketMessage]], None] | Callable[[str | bytes], None],\n    close_timeout: int = 1,\n    **kwargs: Any,\n) -\u003e None: ...\n```\n\nOne smaller typing improvement: `run()` currently leaves `**kwargs` unknown for\nPyright/Pylance. Annotating it as `**kwargs: Any` and adding `-\u003e None` would avoid\n\"partially unknown\" warnings.\n\nThanks.\n","author":{"url":"https://github.com/aircozy","@type":"Person","name":"aircozy"},"datePublished":"2026-06-02T13:45:13.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/1022/client-python/issues/1022"}