With¶

with expr: and with expr as name: are the calling side of Lucid's context-manager machinery, and neither changes from Python: both work exactly as they already do, on anything Context managers's contextmanager produces, or any class declaring contextmanager def __cm__(self):.

This bracketing is also why Lucid has no exactly-once callback-parameter marker, the way some languages do for transaction commits and one-shot completion handlers — see Rejected features.

So every real "make sure this runs exactly once" reduces to a scope Lucid already has: synchronous, contextmanager; asynchronous, await. A callback parameter marked exactly-once would only restate one of the two, with a weaker guarantee at the far end.