| """ |
| Helpers related to (dynamic) resource retrieval. |
| """ |
|
|
| from __future__ import annotations |
|
|
| from functools import lru_cache |
| from typing import TYPE_CHECKING, Callable, TypeVar |
| import json |
|
|
| from referencing import Resource |
|
|
| if TYPE_CHECKING: |
| from referencing.typing import URI, D, Retrieve |
|
|
| |
| _T = TypeVar("_T") |
|
|
|
|
| def to_cached_resource( |
| cache: Callable[[Retrieve[D]], Retrieve[D]] | None = None, |
| loads: Callable[[_T], D] = json.loads, |
| from_contents: Callable[[D], Resource[D]] = Resource.from_contents, |
| ) -> Callable[[Callable[[URI], _T]], Retrieve[D]]: |
| """ |
| Create a retriever which caches its return values from a simpler callable. |
| |
| Takes a function which returns things like serialized JSON (strings) and |
| returns something suitable for passing to `Registry` as a retrieve |
| function. |
| |
| This decorator both reduces a small bit of boilerplate for a common case |
| (deserializing JSON from strings and creating `Resource` objects from the |
| result) as well as makes the probable need for caching a bit easier. |
| Retrievers which otherwise do expensive operations (like hitting the |
| network) might otherwise be called repeatedly. |
| |
| Examples |
| -------- |
| |
| .. testcode:: |
| |
| from referencing import Registry |
| from referencing.typing import URI |
| import referencing.retrieval |
| |
| |
| @referencing.retrieval.to_cached_resource() |
| def retrieve(uri: URI): |
| print(f"Retrieved {uri}") |
| |
| # Normally, go get some expensive JSON from the network, a file ... |
| return ''' |
| { |
| "$schema": "https://json-schema.org/draft/2020-12/schema", |
| "foo": "bar" |
| } |
| ''' |
| |
| one = Registry(retrieve=retrieve).get_or_retrieve("urn:example:foo") |
| print(one.value.contents["foo"]) |
| |
| # Retrieving the same URI again reuses the same value (and thus doesn't |
| # print another retrieval message here) |
| two = Registry(retrieve=retrieve).get_or_retrieve("urn:example:foo") |
| print(two.value.contents["foo"]) |
| |
| .. testoutput:: |
| |
| Retrieved urn:example:foo |
| bar |
| bar |
| |
| """ |
| if cache is None: |
| cache = lru_cache(maxsize=None) |
|
|
| def decorator(retrieve: Callable[[URI], _T]): |
| @cache |
| def cached_retrieve(uri: URI): |
| response = retrieve(uri) |
| contents = loads(response) |
| return from_contents(contents) |
|
|
| return cached_retrieve |
|
|
| return decorator |
|
|
