Function●Since v0.3

swr

Load a cached value using stale-while-revalidate semantics.

This helper is server-side only and is intended for caching internal async dependencies such as auth or metadata lookups.

swr(
  key: str,
  loader: Callable[[], Awaitable[T]],
  *,
  fresh_for: timedelta | None = None,
  max_age: timedelta | None = None,
  model: type[T] | None = None
) -> SWRResult[T]

Semantics:

cache miss: await loader(), store the value, return it
fresh hit (age < fresh_for): return the cached value
stale hit (fresh_for <= age < max_age): return the cached value immediately and trigger a best-effort background refresh
expired (age >= max_age): await loader(), store the value, return it

Parameters

Name	Type	Description
`key`*	`str`	Cache key.
`loader`*	`Callable[[], Awaitable[T]]`	Async callable that fetches the value on miss/revalidation.
`fresh_for`	`timedelta \| None`	Default:`None` How long a cached value is considered fresh (no revalidation). Defaults to `timedelta(0)` so every access triggers a background revalidate while still returning the cached value instantly. Values above :data:`MAX_CACHE_TTL` are clamped to the backend maximum.
`max_age`	`timedelta \| None`	Default:`None` Total lifetime of a cached entry. After this, the next access blocks on the loader. Defaults to :data:`MAX_CACHE_TTL` (24 h by default). Values above :data:`MAX_CACHE_TTL` are clamped to the backend maximum.
`model`	`type[T] \| None`	Default:`None` Optional Pydantic model class. When provided, values are serialized via `model_dump(mode="json")` before storage and deserialized via `model.model_validate()` on read.

View source on GitHub

swr

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