Cache extension

CacheExtension

Base class for persistent caching. Before a node is evaluated, the extension looks up a cache key; on a hit, the result is stored in ExecutionContext.cache and the visitor is skipped.

dynamic_expressions.cache.base.CacheExtension

CachePolicy

A policy defines which node types to cache, how to build keys, and TTL:

dynamic_expressions.cache.base.CachePolicy dataclass

Field	Description
types	Tuple of node classes this policy applies to
key	Callable (node, context) -> str — cache key builder
ttl	timedelta — entry lifetime in the backing store
serializer	Optional per-policy serializer; falls back to default_serializer

from datetime import timedelta

from dynamic_expressions.cache import CachePolicy
from dynamic_expressions.nodes import LiteralNode

policy = CachePolicy[MyContext](
    types=(LiteralNode,),
    key=lambda node, ctx: str(hash(node)),
    ttl=timedelta(minutes=5),
)

When the results depend on context, include context fields in the key:

CachePolicy[UserContext](
    types=(BinaryExpressionNode,),
    key=lambda node, ctx: f"{hash(node)}:{ctx.user_id}",
    ttl=timedelta(minutes=5),
)

RedisCacheExtension

Redis-backed implementation. Requires pip install dynamic-expressions[cache-redis,serialization-msgspec].

dynamic_expressions.cache.redis.RedisCacheExtension

See the Cache cookbook for a full wiring example.

Writing a custom backend

Subclass CacheExtension and implement get_cache / set_cache:

class InMemoryCacheExtension[Context](CacheExtension[Context]):
    def __init__(
        self,
        policies: Sequence[CachePolicy[Context]],
        default_serializer: Serializer[Any],
    ) -> None:
        self.policies = policies
        self.default_serializer = default_serializer
        self._policy_cache = {}
        self._store = {}

    async def get_cache(self, key: str) -> bytes | None:
        return self._store.get(key)

    async def set_cache(self, key: str, value: bytes, policy: CachePolicy[Context]) -> None:
        self._store[key] = value

Use a Serializer compatible with your cached value types.